Method for allocating resources in wireless LAN system and wireless LAN system

ABSTRACT

Provided are a method of allocating resources in a wireless local area network (WLAN) system and the WLAN system including an access point (AP) to allocate a resource for communication between a relay and a station associated with the relay, the relay to allocate a restricted access window (RAW) or a slot for communication with a station based on the allocated resource, and the station to communicate with the relay based on the allocated RAW or the allocated slot.

TECHNICAL FIELD

The present invention relates to a method of allocating resources in awireless local area network (WLAN) system.

BACKGROUND ART

A recent wireless local area network (WLAN) system adopts a slottedchannel access to reduce collisions between stations during an operationof a basic service set (BSS) including thousands of stations. Whenthousands of stations access a channel and attempt to performtransmission at the same time, a collision probability may increase. Inthe slotted channel access method, a restricted access window (RAW) maybe set to prevent collisions, and a transmission duration in the RAWtransmission duration may be divided into slots. A slot in whichtransmission is allowed may be allocated to each station. A station maybe allowed to contend for transmission in a slot allocated to thestation. Thus, a sudden surge of channel accesses may be distributed,and collisions may be reduced.

In addition, the WLAN system introduces a relay operation to extend thecoverage of an access point (AP). In a case in which the relay operationis employed, the slotted method may be adopted to efficiently supporttransmission of a large number of stations.

DISCLOSURE OF INVENTION Technical Solutions

According to an aspect, there is provided a wireless location areanetwork (WLAN) system including an access point (AP) to allocate aresource for communication between a relay and a station associated withthe relay, the relay to allocate a restricted access window (RAW) or aslot for communication with a station based on the allocated resource,and the station to communicate with the relay based on the allocated RAWor the allocated slot.

According to an aspect, there is provided an AP including a resourceallocator to allocate a resource for communication between a relay and astation associated with the relay, and a communication unit to transmit,to the relay, resource allocation information on the allocated resource.

According to an aspect, there is provided a relay including a resourceallocator to allocate a resource for communication between the relay anda station associated with the relay based on resource allocationinformation received from an AP, and communication unit to transmitinformation on the allocated resource to the station.

According to an aspect, there is provided a station including acontroller to identify a resource allocated to the station based on abeacon received from a relay, and a communication unit to communicatewith the relay based on the identified resource.

According to an aspect, there is provided a method of allocatingresources in a WLAN system including an AP, a relay, and a station, themethod performed by the AP, the method including allocating a firstresource for communication between the AP and the relay, andcommunication between the AP and a station associated with the AP, andallocating a second resource for communication between the relay and astation associated with the relay.

The method may further include transmitting, to the relay, resourceallocation information on the allocated second resource.

The method may further include adjusting the allocated second resourcebased on interference information received from the relay.

The method may further include adjusting the allocated second resourcebased on station information received from the relay.

The method may further include transmitting, to the relay, a beaconincluding information on the allocated first resource and information onthe associated second resource.

According to an aspect, there is provided a method of allocatingresources in a WLAN system including an AP, a relay, and a station, themethod performed by the relay, the method including receiving resourceallocation information from the AP, and allocating a resource forcommunication between the relay and a station associated with the relaybased on the received resource allocation information.

The method may further include transmitting, to the station, a beaconincluding information on the allocated resource.

According to an aspect, there is provided a communication methodperformed by a station in a WLAN system including an AP, a relay, andthe station, the method including identifying a resource allocated tothe station based on a beacon received from the relay, and communicatingwith the relay based on the identified resource.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example of a method of transmitting data using arelay in a wireless local area network (WLAN) system according to anembodiment.

FIG. 2 illustrates an example of a configuration of a basic service set(BSS) in a case in which a relay operation is employed according to anembodiment.

FIG. 3 illustrates an example of a method using a restricted accesswindow (RAW) in a case in which a relay is used according to anembodiment.

FIG. 4 illustrates another example of a method using a RAW in a case inwhich a relay is used according to an embodiment.

FIG. 5 illustrates still another example of a method using a RAW in acase in which a relay is used according to an embodiment.

FIG. 6 illustrates a RAW structure in a slotted transmission methodaccording to an embodiment.

FIG. 7 illustrates an example of sharing the same RAW using differentchannels according to an embodiment.

FIGS. 8 and 9 illustrate examples of allocating a plurality of clustersto a single RAW based on offset information according to an embodiment.

FIG. 10 illustrates a method of allocating an allocation identifier(AID) to a cluster according to an embodiment.

FIG. 11 illustrates an allocation location of a beacon transmitted by arelay access point (R-AP) according to an embodiment.

FIG. 12 illustrates a method of allocating slots to stations accordingto an embodiment.

FIG. 13 illustrates more simplified leveled slot allocation according toan embodiment.

FIG. 14 illustrates a RAW allocation method for a relay in a case inwhich a plurality of relays is used according to an embodiment.

FIG. 15 illustrates an example of a RAW allocation method in a case inwhich a plurality of relays is used according to an embodiment.

FIG. 16 illustrates an example of a RAW allocation method for a relay ina case in which a plurality of relays is used according to anotherembodiment.

FIG. 17 illustrates a generalized example of a leveled slot allocationmethod according to an embodiment.

FIG. 18 illustrates an example of a leveled slot allocation method usingan empty slot according to an embodiment.

FIG. 19 illustrates an example of a leveled slot allocation method usingan empty slot according to another embodiment.

FIG. 20 illustrates an example of a leveled slot allocation method usingan empty RAW according to an embodiment.

FIG. 21 illustrates an example of a leveled slot allocation method usingan empty RAW according to another embodiment.

FIG. 22 illustrates an example of a leveled slot allocation method usinga sub RAW according to an embodiment.

FIG. 23 illustrates a generalized example of a leveled slot allocationmethod according to another embodiment.

FIG. 24 illustrates an example of a leveled slot allocation method usinga delegated restricted access window (DRAW) according to an embodiment.

FIG. 25 illustrates another example of a leveled slot allocation methodusing a DRAW according to an embodiment.

FIGS. 26 through 28 illustrate examples of a DRAW allocation method in acase in which a leveled slot allocation method is employed according toan embodiment.

FIG. 29 illustrates an example of allocating a frequency subband to arelay according to an embodiment.

FIG. 30 illustrates a case in which frequency selective transmission(FST) is used in a cluster when a subband for a relay is allocatedaccording to an embodiment.

FIG. 31 illustrates an example of sharing a RAW using differentfrequency subbands according to an embodiment.

FIG. 32 illustrates an example of transmitting data using differentfrequency subbands according to an embodiment.

FIGS. 33 through 36 illustrate examples of a method of sharing a RAWusing different frequency subbands in a leveled slot allocation methodusing an empty slot according to an embodiment.

FIG. 37 illustrates an example of a method of performing RAW sharing ina case in which clusters are spatially separated according to anembodiment.

FIG. 38 illustrates an example of a method of performing RAW sharingusing a time domain according to an embodiment.

FIG. 39 illustrates an example of allocating a plurality of frequencysubbands according to an embodiment.

FIG. 40 illustrates an example of allocating a plurality of frequencysubbands according to another embodiment.

FIG. 41 illustrates an example of a format of a relay resourceallocation IE of Table 3 according to an embodiment.

FIG. 42 illustrates an example of allocating resources for each timeduration according to an embodiment.

FIG. 43 illustrates an example of performing transmission using a relayresource allocation IE in a single frequency subband according to anembodiment.

FIG. 44 illustrates another example of performing transmission using arelay resource allocation IE in a single frequency subband according toan embodiment.

FIG. 45 illustrates an example of performing transmission using a relayresource allocation IE in multiple frequency subbands.

FIG. 46 illustrates an example of allocating a relay transmissionduration according to an embodiment.

FIG. 47 illustrates a format for a frame request according to anembodiment.

FIG. 48 illustrates a format for a frame report according to anembodiment.

FIG. 49 illustrates an example of a format of a management request fieldaccording to an embodiment.

FIG. 50 illustrates an example of a format of a management report fieldaccording to an embodiment.

FIG. 51 illustrates a method of measuring an interference level from aneighboring relay or a neighboring relay BSS using a framerequest/response according to an embodiment.

FIG. 52 illustrates a configuration of an AP according to an embodiment.

FIG. 53 illustrates a configuration of a relay according to anembodiment.

FIG. 54 illustrates an STA according to an embodiment.

FIG. 55 is a flowchart illustrating a resource allocation methodperformed by an AP according to an embodiment.

FIG. 56 is a flowchart illustrating a resource allocation methodperformed by a relay according to an embodiment.

FIG. 57 is a flowchart illustrating a communication method performed byan STA according to an embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, exemplary embodiments will be described with reference tothe accompanying drawings. It is to be understood that the detaileddescription, which will be disclosed along with the accompanyingdrawings, is intended to describe exemplary embodiments of the presentinvention, and is not intended to describe a unique embodiment throughwhich the present invention can be carried out. The following detaileddescription includes detailed matters to provide full understanding ofthe present invention. However, it will be apparent to those skilled inthe art that the present invention can be carried out without thedetailed matters.

The following embodiments are proposed by combining constituentcomponents and characteristics of the present invention according to apredetermined format. The individual constituent components orcharacteristics should be considered to be optional factors on thecondition that there is no additional remark. The individual constituentcomponents or characteristics may not be combined with other componentsor characteristics. Also, some constituent components and/orcharacteristics may be combined to implement the embodiments of thepresent invention. The order of operations to be disclosed in theembodiments of the present invention may be changed. Some components orcharacteristics of any embodiment may also be included in otherembodiments, or may be replaced with those of the other embodiments.

In the following description, specific terminologies used forembodiments of the present invention are provided to help theunderstanding of the present invention. And, the use of the specificterminology can be modified into another form within the scope of thetechnical idea of the present invention.

In some cases, to prevent ambiguity in the concept of the presentinvention, structures and apparatuses of the known art will be omitted,or will be shown in the form of a block diagram based on main functionsof each structure and apparatus. Also, the same reference numerals willbe used throughout the drawings and the specification to refer to thesame or like parts.

Embodiments of the present invention are supportable by standarddocuments disclosed in at least one of wireless access systems includingan Institute of Electrical and Electronics Engineers (IEEE) 802 system,a third generation partnership project (3GPP) system, a 3GPP long termevolution (3GPP LTE) system, and a third generation partnership project2 (3GPP2) system. In particular, the steps or parts, which are notexplained to clearly reveal the technical idea of the present invention,in the embodiments of the present invention can be supported by theabove documents. Moreover, all terminologies disclosed in the presentdisclosure can be supported by the standard documents.

The following embodiments of the present invention can be applied to avariety of systems using wireless access technologies, for example, CodeDivision Multiple Access (CDMA), Frequency Division Multiple Access(FDMA), Time Division Multiple Access (TDMA), Orthogonal FrequencyDivision Multiple Access (OFDMA), Single Carrier Frequency DivisionMultiple Access (SC-FDMA), and the like. The CDMA may be implementedwith radio technologies, for example, Universal Terrestrial Radio Access(UTRA) and CDMA2000. The TDMA may be implemented with radiotechnologies, for example, Global System for Mobile communications(GSM)/General Packet Radio Service (GPRS)/Enhanced Data Rates for GSMEvolution (EDGE). The OFDMA may be implemented with radio technologies,for example, IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, andEvolved UTRA (E-UTRA). For clarity, the following description focuses onthe IEEE 802.11 system. However, technical features of the presentinvention are not limited thereto.

FIG. 1 illustrates an example of a method of transmitting data using arelay in a wireless local area network (WLAN) system according to anembodiment.

In a case in which an access point (AP) transmits data or a frame to astation (STA), a transmission efficiency may be reduced by an obstaclebetween the AP and the STA. In a case in which a STA transmits data toan AP, the STA may not transmit the data properly to the AP since ingeneral a STA has a lower transmission power than an AP. To resolve suchan issue and extend a coverage for data transmission between an AP andan STA, a relay may be used.

In FIG. 1, an STA 1 and an STA 3 are remote from an AP. Thus, datatransmitted from the STA 1 and the STA 3 may not reach the AP orintensities of signals may be weakened. By forwarding the datatransmitted from the STA 1 and the STA 3 using a relay 1 and a relay 2,such issues may be resolved. A relay may be used for uplink (UL)transmission, and downlink (DL) transmission from an AP to an STA.

In a case of a relay operation using a slotted method in a WLAN system,efficient resource allocation, for example, efficient restricted accesswindow (RAW) operation, transmission slot allocation, transmission timeduration allocation, and subband allocation, may be required to increasea transmission efficiency. To increase the transmission efficiency, aRAW and a transmission slot may be properly allocated so that a largenumber of STAs may transmit data without collisions. In addition,simultaneous data transmission may need to be performed using a methodof sharing the same RAW or transmission slot among a greater number ofSTAs, or using a method using different subbands in the same timeduration.

FIG. 2 illustrates an example of a configuration of a basic service set(BSS) in a case in which a relay operation is employed according to anembodiment.

A WLAN system may include an AP, a relay, and an STA. A range of a BSSof the AP may be extended by the relay. An access point may be referredto as an AP, root AP, or Rt-AP. A relay may be referred to as a relayAP, relay STA, or R-AP. A station may be referred to as an STA, andinclude a variety of communication terminals that may be associated withthe AP or the relay.

A BSS of the AP may be referred to as a root AP BSS. The relay mayconstitute a relay BSS that is a BSS of the relay. In the relay BSS, therelay may act as an AP with respect to the STA. The root AP BSS mayoverlap the relay BSS. The root AP BSS indicates an area in which theSTA may maintain communication with the root AP, and the relay BSSindicates an area in which the STA may maintain communication with therelay. A communication area of the root AP BSS may be extended by therelay. A BSS of the root AP with an area extended by the relay may bereferred to as an extended BSS. The extended BSS may include the root APBSS, and the relay BSS of the relay associated with the root AP.

The root AP may inspect an overall network state of the WLAN system. Theroot AP and the relay may transmit beacons including information on anallocated resource. The beacon transmitted by the root AP may bereferred to as a root beacon, Rt-beacon, or root AP beacon. The beacontransmitted by the relay may be referred to as a relay beacon, orR-beacon. The STA may be associated with the root AP through the relay,or directly associated with the root AP.

The AP may generate a single BSS, and the BSS may include a large numberof STAs. In general, an STA may transmit data directly to an AP, like anSTA M of FIG. 2. However, an STA may exchange data with the AP through arelay for range extension. A number of relays may be associated with asingle AP, and each relay may relay, to the AP, data transmitted andreceived from a plurality of STAs.

In a case in which a relay is used to extend the coverage, a slottedtransmission method may be employed when a large number of STAs areincluded in the BSS. In addition, an efficient slot allocation methodand operation performed in view of relay-involved transmission may beneeded.

FIG. 3 illustrates an example of a method using a RAW in a case in whicha relay is used according to an embodiment.

Examples of a method of allocating a resource, for example, a RAW and aslot, in a case in which data is transmitted using a relay will bedescribed hereinafter.

A first example of the resource allocation method is a method ofallocating a RAW for each of transmission between an STA and a relay andtransmission between a relay and an AP, which is illustrated in FIG. 3.Hereinafter, the transmission between an STA and a relay may be referredto as “bottom hop” transmission, and the transmission between a relayand an AP will be referred to as “top hop” transmission.

Referring to FIG. 3, a RAW 1 may be allocated for bottom hoptransmission, and a RAW 2 may be allocated for top hop transmission. Inthe RAW 1, each of an STA 1, an STA 2, and an STA 3 may transmit data toa relay 1 (R1) or a relay 2 (R2) that is used by the each correspondingSTA. In the RAW 2, the relay 1 and the relay 2 may transmit data to anAP. In this example, the UL transmission and the DL transmission mayalso be performed in a single RAW.

FIG. 4 illustrates another example of a method using a RAW in a case inwhich a relay is used according to an embodiment.

Another example of the resource allocation method is a method ofallocating a RAW for each single STA-relay-AP. The STA-relay-AP may bereferred to as a “parent tree”.

Referring to FIG. 4, a RAW 1 may be allocated for transmission between arelay 1 (R1) and an STA 1, an STA 3, and an STA 5 using the relay 1, andtransmission between the relay 1 and an AP. A RAW 2 may be allocated fortransmission between a relay 2 (R2) and an STA 2, an STA 4, an STA 6,and an STA 8 using the relay 2, and transmission between the relay 2 andan AP.

RAW and slot allocation information may be transferred using a beacon.In this example, the beacon may be used to transfer RAW and slotallocation information related to an AP and an STA not using a relay,RAW and slot allocation information related to a relay, and RAW and slotallocation information on a RAW and a slot in which transmission of therelay and the STA is allowed.

FIG. 5 illustrates still another example of a method using a RAW in acase in which a relay is used according to an embodiment.

Still another example of the resource allocation method is a method inwhich a root AP may transmit a root beacon in a BSS, each relay maytransmit a beacon, and an STA using the each corresponding relay mayinclude RAW and slot allocation information in the beacon transmitted bythe each corresponding relay, and transmit the beacon. The RAW and slotallocation information may correspond to information on a RAW and a slotin which UL or DL transmission with the relay is allowed. The beacontransmitted by the each corresponding relay may be referred to as arelay beacon.

RAW and slot allocation for transmission between the relay and the rootAP and transmission between the root AP and an STA not using the relaymay be performed by the root AP. The transmission between the root APand an STA not using the relay may refer to transmission performed bythe root AP to transmit and receive data directly to and from the STA.The transfer of the RAW and slot allocation information may be performedusing the beacon transmitted by the root AP. The transfer of the RAW andslot allocation information may be referred to as “level-0 slotallocation”, and the beacon transmitted by the root AP may be referredas a “root beacon”. In the transmission between the relay and the STA,for example, bottom hop transmission, the corresponding relay directlyinvolved in the transmission between the relay and the STA may allocatea RAW and a slot, and perform transmission of RAW and slot allocationinformation using a relay beacon. The transmission of RAW and slotallocation information may be referred to as “level-1 slot allocation”.

The relay may exchange information with the root AP for the level-1 slotallocation, and the root AP may allocate, to the corresponding relay, anoptimized length of time duration based on the exchanged information.The optimized length of the time duration may refer to a time durationindependent from a RAW, a slot, or a RAW/slot for the root AP. The relaymay directly allocate, based on the exchanged information, a RAW or aslot to be used for transmission between the relay and an STA within thetime duration allocated for the transmission between the relay and theSTA.

The root AP may directly perform the level-1 slot allocation, andprovide level-1 slot allocation information to the relay, and the relaymay transfer the level-1 slot allocation information using a beacon.However, a RAW or a slot to be used for the transmission between therelay and the STA may be allocated directly by the relay. Since therelay may be more aware of information related to STAs directlyassociated with the relay than the root AP, the relay may perform thelevel-1 slot allocation more efficiently. Thus, the root AP may allocatea transmission duration for transmission between the relay and the STA,and delegate, rather than directly performing, detailed RAW/slotallocation within the allocated transmission duration to thecorresponding relay. Hereinafter, the foregoing operation will bereferred to as “leveled slot allocation” or “leveled RAW allocation”.

Due to the extension of the range of the BSS using the relay, an STAassociated with the relay may not receive the root beacon. In a case inwhich RAW/slot allocation information to be used for the transmissionbetween the relay and the STA is included in a relay beacon, thecorresponding STA may only have to receive the relay beacon, rather thanreceiving the root beacon. In addition, since only the RAW/slotallocation information to be used for the transmission between the relayand the STA may be included in the relay beacon, a length of the relaybeacon may be reduced.

The leveled slot allocation method or the RAW allocation method mayinclude a method (A) in which the root AP allocates resources, forexample, a relay transmission duration, and a relay transmissionsubband, at a level 0 in a form of a delegated RAW (DRAW), and allocatesa DRAW duration to the relay, and a method (B) in which the root APallocates resources, for example, the relay transmission duration, and atransmission band, to the relay separately from the RAW for the root APbased on separate resource allocation information not in a form of aRAW.

<(A) Method in which a Root AP Allocates Resources, for Example, a RelayTransmission Duration, and a Relay Transmission Subband, at a Level 0 ina Form of a DRAW, and Allocates a DRAW Duration to a Relay (Method Usinga DRAW)>

FIG. 5 illustrates an example of a method of allocating a slot for eachlevel in a case in which a relay transmits a beacon, in the case of aDRAW.

At a level 0 on the top, a root AP may directly allocate a RAW and aslot. The root AP may allocate a RAW and a slot for transmission betweenthe root AP and a relay, and a RAW and a slot for transmission betweenthe root AP and an STA performing transmission and reception directlywith the AP not using the relay. Since the relay may collect datatransmitted from a number of STAs through bottom hop transmission andtransmit the collected data to the AP, a longer transmission period maybe allocated. To allocate a longer transmission period to the relay,many slots or an overly long single slot may be allocated to the relay.In the example of FIG. 5, UL transmission and DL transmission are set tobe performed in separate RAWs. However, UL transmission and DLtransmission may also be performed through a single RAW. In addition,transmission to a normal STA, and transmission to a relay are includedin a UL RAW and a DL RAW. However, only transmission with the relay maybe included in a single RAW.

At a level 1 on the bottom, each relay may allocate a RAW and a slot fortransmission with an STA using the corresponding relay. Each relay maymanage a level-1 slot, and may include, in a beacon to be transmitted bythe corresponding relay, slot allocation information for thetransmission between the relay and the STA, and transfer the beacon. Arelay may exchange RAW and slot allocation information with an AP forefficient RAW and slot allocation. Although the AP may perform level-1RAW and slot allocation, and provide RAW and slot allocation informationto the relay, it may be more efficient for the relay to directly performRAW/slot allocation for the transmission between the relay and the STA.

At the level 1, another STA or another relay using the same channel maybe disallowed to transmit and receive data to and from an AP while therelay is transmitting and receiving data to and from the STA. To preventcollisions, a root beacon including level-0 RAW and slot allocationinformation of the root AP, and information on a duration in whichtransmission is performed at the level 1 may be transferred. Theduration in which transmission is performed at the level 1 may bereferred to as an “empty slot”, “empty RAW”, or “delegated RAW”.

To determine an empty slot duration at the level 0, the AP may exchangeinformation with the relay. The empty slot duration may also be referredto as an empty RAW duration, or DRAW duration. The empty slot durationfor UL transmission may be set based on an amount of data to betransmitted by the relay to the AP. Accordingly, the AP may receiveuplink data indication (UDI) information from the relay, and set theempty slot duration. The AP may be previously aware of an amount of DLdata received by STAs using the relay. Thus, to set the empty slotduration for DL transmission, the AP may set the empty slot durationbased on the amount of the data received by the STAs using the relay,and inform the relay of the set empty slot duration.

In the example provided above, the empty slot duration for ULtransmission is separated from the empty slot duration for DLtransmission. However, the empty slot duration for UL transmission andthe empty slot duration for DL transmission may be set as a single emptyRAW, and the relay may allocate an UL RAW, a DL RAW, and a power savepoll (PS-Poll) RAW at a proper ratio within the single empty RAW, asnecessary. The single empty RAW may also be referred to as a singleDRAW. In this example, the relay may distribute and use slots properlybased on an amount of UL or DL data transmitted and received to and froman STA associated with the relay.

In a case in which an amount of traffic is relatively constant andtransmission is performed periodically, for example, in a sensor networkor a smart grid service, an AP may initially allocate a RAW and a slotin a uniform pattern, and provide RAW/slot allocation information. Inthis example, a periodic RAW (PRAW) may be used for the RAW and slotallocation. For example, a RAW, for example, a DRAW, to be used fortransmission between a relay and an STA may be allocated to a fullbeacon to be transmitted occasionally. In a case in which relayallocation information is unchanged, relay RAW allocation informationmay not be specified separately in a short beacon to be transmittedsubsequent to the full beacon.

The foregoing example may be applied to two-hop relay transmissionperformed using a single relay. In a case of multi-hop transmissionperformed using a number of relays, a lower level may be set tocorrespond to a relay level, and a level may be extended using the samemethod described above.

In the example of FIG. 5, an empty slot for a single relay may beallocated in a RAW. However, empty slots for a number of relays may beallocated in a single RAW, or empty slots for each relay may beallocated in the entire single RAW.

A relay beacon may be transmitted by each relay, and transmittedperiodically. For example, after a beacon of a root AP is transmitted, arelay beacon may be transmitted in a RAW or slot allocated by the rootAP to the corresponding relay. The allocated RAW or slot may correspondto a first empty slot for the corresponding relay of a level 0.

The relay may aggregate data received from each STA using the relay andtransmit the aggregated data to the root AP, whereby a transmissionefficiency may increase. The root AP may aggregate and transmit data,related to a number of STAs, to be transmitted using the relay. Therelay may divide data received from the root AP for each STA andtransmit the divided data to the corresponding STA, whereby thetransmission efficiency may increase. To achieve the foregoing,conventional data aggregation technologies, for example, anaggregation-medium access control (MAC) service data unit (A-MSDU), andan aggregation-MAC protocol data unit (A-MPDU), may be used.

In the slot allocation method described above, when the same RAW and thesame slot are enabled to be shared by a greater number of STAs,utilization of the slot may increase and the transmission efficiency mayincrease. For example, when the STAs are enabled to transmit and receivedata at the same time, the transmission efficiency may increase further.

FIG. 6 illustrates a RAW structure in a slotted transmission methodaccording to an embodiment.

A number of RAWs included in a single beacon period may be restricted,and the restricted number of RAWs may be insufficient to performtransmission in each cluster. A cluster refers to a unit that includes arelay and STAs using the relay.

To resolve an issue of the restricted number of RAWs and efficientlyutilize the RAWs, the following methods may be employed.

(1) Allocation of a Number of Clusters to a Single RAW in a Time Domain

When a few STAs are included in a cluster, a number of clusters may beallocated to a single RAW. In this example, although STAs of a number ofclusters are allocated to a single RAW, a probability of collisions maybe relatively low since the total number of the STAs is not great. EachSTA may contend for channel allocation, and data may be transmitted in achronological order in which a channel is allocated to each STA. In acase in which transmission is not completed in a time duration allocatedto a predetermined relay cluster, a RAW allocated to be usedsimultaneously by a number of clusters may be used to additionallytransmit remaining data in a shared time duration.

(2) Allocation of a Number of Clusters to a Single RAW in a SpatialDomain

When clusters are remote from each other, a single RAW may be allocatedto the spatially separated clusters so that simultaneous datatransmission may be performed.

For example, referring to FIG. 1, a cluster 1 including the relay 1 anda cluster 2 including the relay 2 may be allocated to the same RAW. InFIG. 1, the STA 1 and the STA 2 are spatially separated from each other.UL transmission performed by the STA 1 to transmit data to the relay 1and UL transmission performed by the STA 2 to transmit data to the relay2 may be performed simultaneously. Such simultaneous transmission may bereadily applied to a transmission duration between each relay and an STAusing the each corresponding relay.

(3) Allocation of a Number of Clusters to a Single RAW in a FrequencyDomain

Clusters may be enabled to perform transmission and reception with anSTA using different channels. As shown in FIG. 7, when transmissionbetween a relay 1 and STAs in a cluster 1 including the relay 1 isperformed using a channel 3 (CH3) and a channel 4 (CH4), andtransmission between a relay 2 and STAs in a cluster 2 including therelay 2 is performed using a channel 1 (CH1) and a channel 2 (CH2),simultaneous data transmission may be performed, and the two clustersmay be allocated to a single RAW. FIG. 7 illustrates an example ofsharing the same RAW using different channels according to anembodiment. The example may be useful in a case in which a relativelynarrow bandwidth (BW) is used, for example, in a sensor network or asmart grid.

Such simultaneous transmission may be readily applied to a level-1transmission duration in which transmission between a relay and an STAusing the relay is performed.

When simultaneous transmission is performed, communication between an APand the relay 1 or the relay 2 may be performed using all of thechannels (CH1 to CH4). A relay may aggregate data received from each STAand transmit the aggregated data using a wider channel, whereby atransmission efficiency may increase.

As shown in FIG. 5, in the leveled slot allocation method of allocatinga slot for each level, information exchange between a relay and an AP,and traffic information exchange of STAs may be performed for the mostefficient utilization of a RAW and a slot. In a case in which STAscontinuously join and leave a BSS, or in a case in which STA grouping isre-performed, RAW and slot allocation may need to be changed, which mayact as overhead.

The RAW sharing methods (1) to (3) may also be applied to a case inwhich the method (B) in which the root AP allocates resources, forexample, the relay transmission duration, and a transmission frequencyband, to the relay separately from the RAW for the root AP based onseparate resource allocation information not in a form of a RAW, isused.

In a case in which the method (B) is used in relation to the method (1)of allowing simultaneous transmission in a time domain, relays that maysimultaneously perform transmission within a cluster in a time domainmay be allocated to the same transmission duration. The transmissionduration allocated to be used simultaneously in a number of clusters maybe used to additionally transmit remaining data within a shared timeduration in a case in which transmission is not completed within thetime duration allocated to a predetermined relay cluster.

In a case in which the method (B) is used in relation to the method (2)of allowing simultaneous transmission in a spatial domain, atransmission time may be allocated to relays that may simultaneouslyperform transmission in spatially separated clusters so thattransmission may be performed at the same time. Transmission indifferent clusters that are separated by a sufficient distance andhardly affected by each other may be performed separately at the sametime. A transmission time duration for transmission between thespatially separated clusters may not be aligned based on a mutualtransmission time duration.

In a case in which simultaneous transmission is performed usingdifferent frequency subbands, a method similar to the method (B) may beapplied. Different relays may be set to perform transmission in acluster using different subbands. In a case in which a root AP uses asubband different from the subbands used by the relays, transmissionbetween the root AP and a relay or an STA directly associated with theroot AP may be performed simultaneously with transmission in each relaycluster. When a subband used for transmission performed by the root APis different from a subband used for transmission in each relay cluster,a transmission duration may not be adjusted, and data may be transmittedseparately at the time same in respectively allocated subbands. In thisexample, a time duration may be allocated to prevent a relay and an STAusing the same subband from simultaneously performing transmission.

The methods (1), (2), and (3) may be applied all together. For example,by allocating different subbands, a root AP and a plurality of relaysmay simultaneously perform transmission in a cluster. When relays usingthe same subband are spatially separated from each other and hardlyaffected by each other, the relays may simultaneously performtransmission. In a case in which a few STAs belong to a single clusteralthough the same subband is used, a number of clusters may be allocatedto a single RAW.

(4) Allocation of a Plurality of Clusters to a Single RAW Based onOffset Information

Referring to FIG. 8, a method of allocating a plurality of clustersincluding a single R-AP and a plurality of STAs to a single RAW durationbased on an allocation offset (AO) value may be used. FIGS. 8 and 9illustrate examples of allocating a plurality of clusters to a singleRAW based on offset information according to an embodiment.

As shown in FIGS. 8 and 9, in a case in which four RAWs, for example, aRAW 0 to a RAW 3, are allocated within a beacon interval of an Rt-AP,and four clusters are allocated to each RAW, an R-AP may calculate anallocation location of the R-AP based on the following values.

-   -   Information included in Rt-AP beacon frame    -   ASN (Allocation Sequence Number): 1 octet    -   AIO (Allocation Interval Order): 4 bit    -   R-AP parameters    -   Allocated RAW number: 1 octet    -   AO (Allocation Offset): 1 octet (0<=AO<=2^(AIO+1)−1)    -   R-AP Location: current ASN % 2^(AIO+1)==AO

When a currently received beacon ASN of the Rt-AP corresponds to acurrent ASN, and a result value of “current ASN % 2^(AIO+1)” matches avalue of the AO allocated from the Rt-AP, a current beacon duration maybe determined to be a duration allocated to a predetermined R-AP. Inaddition, the R-AP may identify an accurate allocation location based ona location value of a RAW allocated by the Rt-AP.

In FIG. 9, calculation may be performed based on allocation parametersshown in FIG. 9. Referring to FIG. 9, in a case in which an ASNcorresponds to “0, 4, 8, . . . ”, a RAW may be allocated to an R-APhaving an allocation identifier (AID) of 64. In a case in which an ASNcorresponds to “1, 5, 9, . . . ”, a RAW may be allocated to an R-APhaving an AID of 2176 may correspond to an allocation duration of theR-AP.

FIG. 10 illustrates a method of allocating an AID to a cluster accordingto an embodiment.

An R-AP in each cluster may be allocated a block AID in a process ofbeing associated with an Rt-AP. As shown in FIG. 10, the block AID maybe allocated using an AID structure in page units, block index units,and sub-block index units. In this example, a first AID value of theallocated block AID may be set to be an AID of the R-AP. Remaining AIDvalues, excluding the AID of the R-AP, within a determined range may beallocated to STAs in a cluster when the STAs request association. Byallocating an AID for each cluster or each level in a 2-hop network, anAP may simply allocate and efficiently manage AIDs. In the example ofFIG. 10, each RAW may be allocated in page ID units, and allocated inblock index units for each cluster. Thus, an R-AP in each cluster maymanage a total of 64 block AIDs including its own AID. In such astructure, a single R-AP may accommodate up to 63 STAs.

FIG. 11 illustrates an allocation location of a beacon transmitted by anR-AP according to an embodiment.

FIG. 11 illustrates an example of an allocation location of a beacon ofthe R-AP in a case in which a RAW is allocated in cluster or tree levelunits. Each RAW may start with a beacon of the R-AP, and be configuredbased on the number of slots having the same lengths. The allocationlocation of the beacon of the R-AP may be automatically determined basedon such a configuration, and a length of the RAW and locationinformation may be determined by an Rt-AP.

FIG. 12 illustrates a method of allocating slots to stations accordingto an embodiment.

Referring to FIG. 12, slots for STAs may be allocated within a RAWduration.

In FIG. 12, an R-AP (R1) may transfer allocation information to an STArequesting association to R1, and the STA may be allocated a slot simplywithout performing a separate procedure for allocation. The allocationinformation transferred from R1 to the STA may include information asfollows.

-   -   Information included in R-AP beacon frame    -   Length information of slot, the total number of slots    -   STA Slot Allocation bitmap (0: Empty slot, 1: Allocated slot)    -   STA slot allocation info: allocated by R-AP in association        process    -   Allocated slot number

The STA may transmit and receive data to and from the R-AP in the slotduration allocated to the STA. In a case in which DL data, for example,data transmitted from the R-AP to the STA, is present, the R-AP maytransmit the data using an acknowledgement (ACK) frame or trafficindication map (TIM) information.

FIG. 13 illustrates more simplified leveled slot allocation according toan embodiment.

In a case in which a network configuration is changed relativelyslightly, RAW and slot allocation performed by an AP may be moreefficient to reduce overhead. For such a case, an example of asimplified leveled slot allocation method with less overhead will bedescribed.

FIG. 13 illustrates a RAW configuration for simplified leveled slotallocation. An AP may determine a RAW structure based on the totalnumber of STAs and relay numbers at a beginning of BSS generation. EachRAW may have the same length, and information on the RAW structure mayinclude the following fields in a beacon frame of an Rt-AP.

-   -   Length of RAW    -   Total number of RAWs    -   RAW allocation bitmap (0: Empty RAW, 1: Allocated RAW)    -   RAW type Information (R-AP RAW, Rt-AP RAW, common RAW)

A RAW may be classified based on a RAW type. An R-AP RAW may indicate aduration in which an R-AP and an STA in a cluster may transmit andreceive data exclusively. An Rt-AP RAW may indicate a duration forcommunication between an Rt-AP and an STA managed directly by the Rt-AP.A common RAW may indicate a duration commonly available for all nodesbased on contention.

FIG. 14 illustrates a RAW allocation method for a relay in a case inwhich a plurality of relays is used according to an embodiment.

RAWs for a plurality of relays may be allocated in a beacon interval ofa root AP. A single RAW or a number of RAWS may be allocated to a singlerelay. For example, for STA/relay/root AP transmission, a PS-Poll RAWfor UL and DL resource allocation, a DL RAW, a UL RAW, or a DL/UL RAWfor transmission between an STA and a relay, and a DL RAW, a UL RAW, ora DL/UL RAW for transmission between a root RP and a relay may beallocated as necessary using various combinations thereof. In a case inwhich STAs associated with the relay have different transmissionintervals, RAWs for transmission between a plurality of relays/STAs maybe allocated in a single relay beacon interval.

A transmission duration for transmission from a root AP to another relayor another STA may also be allocated in a relay RAW group for apredetermined relay.

Since a relay may be used for transmission range extension, STAsassociated with the relay may not receive a beacon of the root AP andmay not obtain information on a RAW allocated by the root AP. Thus, eachrelay may receive a root beacon from the root AP, and transfer, to STAsassociated with the corresponding relay, RAW allocation informationrelated to the corresponding relay and slot allocation information to beused for level-1 transmission that are included in the root beacon. Therelay may extract necessary information from the information included inthe root beacon, rather than transferring the information included inthe root beacon. The relay may transmit the extracted informationincluding additional slot allocation information for level-1transmission. Thus, a length of a relay beacon to be transmitted by therelay to an STA may be shorter than a length of the root beacon.

The root AP may include, in the root beacon, RAW allocation informationwith respect to level-0 transmission, and transmit the root beacon. Thelevel-0 transmission may include, for example, transmission between theroot AP and the relay, and transmission between the root AP and an STAdirectly associated with the root AP.

The relay may receive a root AP beacon from the root AP, and identifyRAW allocation information of the root AP from the root AP beacon. Therelay may include, in a relay beacon, RAW allocation informationnecessary for an STA associated with the relay, and transmit the relaybeacon to the STA. For example, the RAW allocation information necessaryfor the STA may include RAW and slot allocation information fortransmission between the relay and the STA, and information on aduration in which transmission between the root AP and the relay isperformed. The STA associated with the relay may receive the relaybeacon, and determine when data is to be transmitted, based on thereceived relay beacon.

FIG. 15 illustrates an example of a RAW allocation method in a case inwhich a plurality of relays is used according to an embodiment.

In FIG. 15, a relay RAW group may indicate RAWs allocated to a singlerelay. In the example of FIG. 15, a beacon of each relay may betransmitted at a point in time at which a first RAW for thecorresponding RAW group starts. The relay may allocate a first RAWimmediately subsequent to transmission of each relay beacon as a PS-PollRAW. An STA may transmit a PS-Poll and a UDI to a relay which the STA isassociated with. To optimize a UL RAW and a DL RAW for transmissionbetween the root AP and the relay and transmission between the relay andthe STA, the relay may transmit the PS-Poll and the UDI to the root AP.

FIG. 16 illustrates an example of a RAW allocation method for a relay ina case in which a plurality of relays is used according to anotherembodiment.

In the example of FIG. 16, the point in time at which the relay beaconis to be transmitted in the example of FIG. 15 is changed to beimmediately subsequent to transmission of a root AP beacon. Beacons ofall relays allocated in a single beacon interval may be transmittedsequentially immediately after the root AP beacon is transmitted, and afirst RAW starting subsequent thereto may be allocated as a PS-Pollduration for a number of relays.

In the example of FIG. 15, a PS-Poll duration may be allocated to eachrelay RAW group. However, in the example of FIG. 16, a single PS-PollRAW may be used, and a PS-Poll and a UDI for all relay transmission maybe transmitted in the PS-Poll RAW. In this example, a separate PS-Pollduration may not be allocated to each relay RAW group.

In this example, by setting a single PS-Poll RAW, a probability of wasteof RAWs may be reduced in comparison to a case in which a separatePS-Poll RAW is allocated to each relay. In addition, an STA searchingfor a relay to be associated with may select an optimal relay within arelatively short time since beacons of relays may be transmittedsequentially immediately after a root AP beacon is transmitted.

The methods of transmitting a relay beacon described above, for example,the method (1) of transmitting a relay beacon at a point in time atwhich a RAW allocated to each relay starts in a case in which points intime at which relay beacons are to be transmitted are distributed, andthe method (2) of transmitting a relay beacon of each relay subsequentto a root AP beacon and preventing each relay RAW from startingimmediately subsequent to the corresponding relay beacon, may beselectively applied to other examples. The distributed relay beacontransmission method or the centralized relay beacon transmission methodmay be applicable to both examples of the method (A) using a DRAW andthe resource allocation method (B) using resource allocationinformation.

In the method of transmitting relay beacons in a distributed manner, arelay RAW may not be immediately subsequent to a relay beacon. Based onrelay RAW scheduling, the relay RAW may be allocated at a point in timefar away from the relay beacon.

In the method of transmitting relay beacons in a centralized manner,relay beacons to be transmitted simultaneously may be transmitted safelyby allocating a separate RAW for relay beacon transmission in a root APbeacon.

FIG. 17 illustrates a generalized example of a leveled slot allocationmethod according to an embodiment.

Referring to FIG. 17, allocation with respect to the entire RAW may beperformed by a root AP, and allocation information on the entire RAW maybe provided through a root beacon. A slot for a RAW corresponding tolevel-0 transmission may be allocated by the root AP. The RAW for thelevel-0 transmission may be allocated by the root AP as an empty RAW oras an empty slot, and detailed slot allocation may not be performed.Hereinafter, the empty RAW may also be referred to as a delegated RAW,and the empty slot may also be referred to as a delegated slot. In theempty RAW or the empty slot of the root beacon, a duration fortransmission between a relay and an STA may be indicated. Based on theduration, occurrence of collisions may be prevented. The collisions mayoccur when another STA transmits data in a transmission duration betweenthe relay and the STA. The slot for the level-1 transmission, forexample, the transmission between the relay and the STA, may beallocated by the relay, and information on the allocated slot may beincluded in a relay beacon.

In the relay beacon, slot allocation information of a RAW for level-0transmission may be omitted. In the relay beacon, the RAW for thelevel-0 transmission may be indicated as an empty RAW or an empty slot.In the empty RAW or the empty slot of the relay beacon, a transmissionduration between the relay and an AP may be indicated, and thetransmission duration may prevent an STA associated with the relay fromtransmitting data while the transmission between the relay and the AP isbeing performed. The STA associated with the relay may receive the RAWallocation information of the relay beacon, and may not receive the rootbeacon.

In FIG. 17, a RAW for relay transmission may include a DL RAW in whichdata is transmitted from the root AP to the relay, a DL and UL RAWbetween the relay and an STA, and an UL RAW in which data is transmittedfrom the relay to the root AP. The DL and UL RAW may indicate a RAW inwhich both DL transmission and UL transmission are possible in a singleRAW. The RAW configuration of FIG. 17 may be provided as an example, andother combinations may also be possible.

The root AP may allocate slots for the DL RAW and the UP RAW. The rootAP may set the DL and UL RAW between the relay and the STA as an emptyRAW. The root AP may include, in a root AP beacon, RAW allocationinformation on the DL and UL RAW between the relay and the STA, andtransmit the root AP beacon.

The relay may receive the root AP beacon, and allocate slots for the DLand UL RAW between the relay and the STA set by the root AP as the emptyRAW. The relay may set the DL RAW and the UL RAW as empty RAWs. Therelay may include RAW allocation information in a relay beacon, andtransmit the relay beacon.

The relay may perform UL or DL transmission with the root AP based onslot allocation information of the root AP in the DL RAW and the UL RAWthat is identified through the root AP beacon.

An STA associated with the relay may perform UL or DL transmission withthe relay based on information on slots allocated in the DL and UL RAWbetween the relay and the STA that is identified through the relaybeacon.

A RAW subsequent to the transmission of the root AP beacon and the relaybeacon may be allocated as a PS-Poll RAW. The STA may transmit a PS-Polland a UDI to the relay, and the relay may transmit the PS-Poll and theUDI to the root AP, whereby the UL RAW and the DL RAW for transmissionbetween the root AP and the relay and transmission between the relay andthe STA may be optimized.

FIG. 18 illustrates an example of a leveled slot allocation method usingan empty slot according to an embodiment.

In the example of FIG. 18, each relay RAW group may include acombination of a PS-Poll RAW, a DL RAW, a UL RA, and a UL/DL RAW.

Each STA may transmit a PS-Poll and a UDI to a relay immediately after aroot beacon and a relay beacon are transmitted. The relay receiving thePS-Poll and the UDI may identify an amount of UL data of the STA andresource allocation requirements, and transmit the PS-Poll and the UDIto a root AP based on the identified amount of UL data and the resourceallocation requirements.

A duration in which the STA transmits the PS-Poll and the UDI to therelay may be set and protected as an empty slot at a level 0, and aduration in which the relay transmits the PS-Poll and the UDI to the APmay be set and protected as an empty slot at a level 1.

The root AP may receive the PS-Poll and the UDI, and adjust slotallocation to be used for UL and DL transmission of the STA and therelay. The root AP may adjust DL slot allocation with respect to thelevel 0 and the level 1 based on PS-Poll information at a start point ofa RAW 2. The root AP may provide slot allocation information at thelevel 0 by transmitting a DL allocation frame. The DL allocation framemay include the slot allocation information at the level 0. In the DLallocation frame, the level-1 transmission duration is allocated as anempty slot. The relay may receive the slot allocation information fromthe root AP, and indicate the slot allocation information at the level 0as an empty slot, rather than including the slot allocation informationat the level 0. The relay may allocate slots during the durationallocated by the root AP as an empty slot at the level 0, and transmitthe slot allocation information through the DL allocation frame at thelevel 1.

The STA may receive DL allocation information, and identify a slotallocated to the STA based on the DL allocation information.

Similarly, the root AP may adjust slot allocation at the level 0 and thelevel 1 using UDI information and a UL allocation frame with respect toan UL RAW.

The empty slot may be indicated in a DL or UL allocation frame or a RAWparameter set information element (RPS IE) included in a beacon. An RPSIE of a root beacon may indicate a relay allowed to perform transmissionin a relay RAW group.

FIG. 19 illustrates an example of a leveled slot allocation method usingan empty slot according to another embodiment.

FIG. 19 illustrates an example of allocating a DL RAW and a UL RAW as asingle RAW, for example, a UL/DL RAW, rather than allocating the DL RAWand the UL RAW as separate RAWs. A root AP may transmit a UL/DLallocation frame to adjust DL and UL slot allocation based on a PS-Polland a UDI received through a relay from an STA. In this example, sincethe DL RAW and the UL RAW may not be separated, the root AP may flexiblyadjust and allocate a UL transmission duration and a DL transmissionduration within the single RAW.

FIG. 20 illustrates an example of a leveled slot allocation method usingan empty RAW according to an embodiment.

Referring to FIG. 20, each relay RAW group may include a combination ofa PS-Poll RAW, a DL RAW, a UL RAW, and a UL/DL RAW, and an empty slotmay be allocated to a single separate RAW.

Each STA may transmit a PS-Poll and a UDI to a relay immediately after aroot beacon and a relay beacon are transmitted. The relay receiving thePS-Poll and the UDI may identify an amount of UL data of the STA andresource allocation requirements, and transmit the PS-Poll and the UDIto a root AP based on the identified amount of UL data and the resourceallocation requirements.

A duration in which the STA transmits the PS-Poll and the UDI to therelay may be set and protected as an empty slot at a level 0, and aduration in which the relay transmits the PS-Poll and the UDI to the APmay be set and protected as an empty slot at a level 1.

The root AP may receive the PS-Poll and the UDI, and adjust slotallocation to be used for UL and DL transmission of the relay. The rootAP may adjust DL slot allocation with respect to the level 0 based onPS-Poll information at a start point of a RAW 2. The root AP may providethe adjusted slot allocation information at the level 0 by transmittinga DL allocation frame including slot allocation information with respectto the level 0.

The relay may adjust DL slot allocation with respect to the level 1based on the PS-Poll information received from the STA at a start pointof a RAW 2′. The relay may provide the adjusted slot allocationinformation at the level 1 by transmitting a DL allocation frameincluding slot allocation information with respect to the level 1.

The relay may adjust UL slot allocation with respect to the level 1based on the UDI information received from the STA at a start point of aRAW 3′. The relay may provide the adjusted slot allocation informationat the level 1 by transmitting a UL allocation frame including slotallocation information with respect to the level 1.

The root AP may adjust UL slot allocation with respect to the level 0based on the UDI information received from the relay at a start point ofa RAW 3. The root AP may provide the adjusted slot allocationinformation at the level 0 by transmitting a UL allocation frameincluding slot allocation information with respect to the level 0.

An empty RAW may be indicated in an RPS IE included in a beacon. An RPSIE of a root beacon may indicate a relay allowed to perform transmissionin a relay RAW group.

FIG. 21 illustrates an example of a leveled slot allocation method usingan empty RAW according to another embodiment.

In FIG. 21, a transmission duration between a relay and an STA may beallocated as a single DL/UL RAW, in contrast to the example of FIG. 20in which the transmission duration is divided into a DL RAW and a ULRAW. In this example, a DL allocation frame for the DL RAW and a ULallocation frame for the UL RAW may not be separated, and a DL and ULallocation frame including UL slot and DL slot information adjustedbased on PS-Poll and UDI information of an STA may be transmitted at astart point of a RAW 2′.

By setting the DL/UL RAW as a single RAW, a UL slot and a DL slot fortransmission between the STA and a relay may be allocated to beflexible, whereby the RAW may be utilized more efficiently. Transmissionin a cluster in which transmission between the relay and the STA isperformed may be performed more efficiently.

FIG. 22 illustrates an example of a leveled slot allocation method usinga sub RAW according to an embodiment.

In the example of FIG. 22, a root AP may allocate a single RAW forsingle relay transmission, include RAW allocation information in a rootAP beacon, and transmit the root AP beacon.

Each relay may divide a single relay RAW allocated to the correspondingrelay into sub RAWs, include sub RAW allocation information in a relaybeacon, and transmit the relay beacon.

The root AP and an STA associated with the relay may determine, based onthe sub RAW allocation information included in the relay beacon, whentransmission between the STA and the relay and transmission between therelay and the AP are performed.

FIG. 23 illustrates a generalized example of a leveled slot allocationmethod according to another embodiment.

Although the example of FIG. 23 is similar to the example of FIG. 17, atransmission duration between a root AP and a relay may be allocated toan arbitrary duration in a form similar to transmission between a normalAP and an STA, rather than being subordinate to a transmission durationbetween the relay and an STA. The example of FIG. 23 is different fromthe examples related to FIG. 17 in that a relay beacon may betransmitted at a point in time at which or at a point in time before aDRAW to be used for transmission between the relay and the STA starts.The DRAW may correspond to an empty RAW at a level 0.

A RAW and slot in the transmission duration between the root AP and therelay, or a RAW and slot in a transmission duration between the root APand an STA directly associated with the root AP may be allocated by theroot AP. RAW and slot allocation information may be transmitted in aform of being included in a root AP beacon. In this example, thetransmission duration between the root AP and the relay may be allocatedto an arbitrary duration in a form similar to transmission between anormal AP and an STA, rather than being subordinate to the transmissionduration between the relay and the STA. The transmission durationbetween the root AP and the relay and the transmission duration betweenthe root AP and the STA directly associated with the root AP may beallocated to a single RAW, or allocated to separate RAWs respectively.

The root AP may allocate the transmission duration between the relay andthe STA by indicating the transmission duration between the relay andthe STA as a DRAW, and delegate detailed RAW/slot allocation to therelay. A root beacon may not include level-1 RAW/slot allocationinformation.

The root AP may allocate a single DRAW or a number of DRAWs for thetransmission between the relay and the STA.

Based on a DRAW, a relay allowed to perform transmission in thecorresponding DRAW, and a transmission allow duration may be identified.In the DRAW, data transmission between a relay that is specified to beallowed to perform transmission and STAs associated with thecorresponding relay may be allowable in principle. Thus, collisionsbetween STAs associated with different relays caused by an extendedservice range in a BSS may be prevented effectively.

For efficient use of a medium, transmission of an STA belonging to aroot BSS may be prohibited with respect to a duration in which an emptyRAW is explicitly set by the root AP, and allowed with respect to theother durations, among DRAW durations. In this example, to protect relaytransmission, the following two methods may be employed.

<1. Protection Method with Respect to a Resource Allocated to AnotherRelay>

A root AP may verify whether a root BSS is spatially separated fromanother relay BSS. When the spatial separation is insufficient, the rootAP may prohibit data transmission of an STA associated with the root APby setting another relay transmission duration as an empty RAW or an APpower management (PM) RAW. The other relay transmission duration maycorrespond to a DRAW duration. In a duration not explicitly set as anempty RAW although the duration corresponds to a DRAW duration, an STAmay transmit data. The root AP may prohibit transmission of apredetermined STA that is greatly affected by interference of the otherrelay BSS, among STAs in the root BSS, rather than prohibiting datatransmission of all of the STAs in the root BSS with respect to theother relay transmission duration. In this example, a method using amodified empty RAW or a modified AP PM RAW that may indicate an STAexplicitly prohibited from performing transmission, or a method ofexcluding an STA prohibited from performing transmission from a targetto be allocated a transmission duration may be used.

The root AP may verify whether a predetermined STA in the root BSS isaffected by interference of the other relay BSS, by receivinginterference information of the STA using “a method of determining aspatial separation between (BB) relays”, which will be described later,or by receiving, directly from an STA, information related to anotherSTA or the other relay BSS that interferes with the STA. The STAaffected by interference may be included in the root BSS and affected byinterference of the other STA or the other relay BSS.

To prevent collisions occurring when an STA belonging to a relay BSSperforms transmission in a transmission duration for another relay BSSusing the same channel, the relay AP may prohibit transmission bysetting the transmission duration of the other relay BSS as an empty RAWor an AP PM RAW. Data transmission of the STA in a duration not set asan empty RAW may be allowed.

The relay BSS may periodically verify whether the relay BSS is spatiallyseparated from the other relay BSS. When it is verified that the spatialseparation is insufficient, the relay BSS may prohibit data transmissionof STAs associated with the relay BSS by setting another relaytransmission duration as an empty RAW or an AP PM RAW.

The relay BSS may prohibit, with respect to the other relay transmissionduration, data transmission of a predetermined STA greatly affected byinterference of the other relay BSS, among STAs in the relay BSS, ratherthan prohibiting data transmission of all the STAs in the relay BSS. Inthis example, a method using a modified empty RAW or a modified AP PMRAW that may indicate an STA prohibited from performing transmission, ora method of excluding an STA prohibited from performing transmissionfrom a target to be allocated may be used.

The relay AP may verify whether a predetermined STA in the relay BSS isaffected by interference of the other relay BSS or another root BSS, byreceiving interference information of the STA using “a method ofdetermining a spatial separation between (BB) relays”, or by receiving,directly from an STA, information related to another STA or the otherrelay BSS that interferes with the STA. The STA may be included in therelay BSS and affected by the interference of the other STA or the otherrelay BSS.

In a case in which there is a frame to be urgently transmitted by theroot AP, transmission in a DRAW duration may be allowed as an exception.In level-1 transmission, an STA may be allowed to perform transmission,as an exception, in a duration (1) in which transmission being performedin the other relay BSS is not sensed, or in a duration (2) in which aRAW is not allocated within a duration allocated for transmission in thecorresponding relay BSS when a beacon of another relay in whichtransmission is being performed is received, although the durationcorresponds to a time duration not allocated to a relay which the STAbelongs to.

An STA belonging to a root AP and an STA belonging to a relay may beallowed to perform transmission through contention, similar totransmission in a conventional overlapping basic service set (OBSS)environment, even in a duration in which transmission of the STAs to anAP is not allowed. However, since a probability of collisions may berelatively high in a case in which data is transmitted in a duration notallocated to a BSS which an STA belongs to, the STA may perform requestto send (RTS)/clear to send (CTS) in advance of data transmission.

The relay or the root AP may explicitly prohibit transmission of STAsassociated with the relay or the root AP by setting, as an empty RAW, aduration in which intense contention or collisions are expected, amongtransmission durations not allocated to the relay or the root AP. Inaddition, the relay AP may prohibit an STA from performing transmissionto a relay in a duration in which transmission between the relay and theroot AP is performed, by setting, as an empty RAW, the duration in whichthe transmission between the relay and the root AP is performed.

<2. Protection Method with Respect to a Resource Allocated to a Relay>

A relay may request a root AP to protect a resource allocated to therelay. In response to the request from the relay, the root AP mayexplicitly prohibit transmission of other predetermined relay BSSs or aportion of STAs in the other predetermined BSSs with respect to theresource allocated to the relay. The portion of the STAs may alsoinclude STAs in a root BSS. The resource allocated to the relay mayinclude, for example, a transmission duration or a duration allocated bythe root AP as a DRAW.

In an example, in a case in which a relay is seriously affected byinterference caused by transmission of another relay BSS, predeterminedSTAs belonging to the other relay BSS, or STAs of the root BSS, anddesires to prohibit the entire or a portion of the STAs of the otherrelay BSS from performing transmission in a transmission durationallocated to the relay, for example, in a case in which the relaydesires protection, the relay may request the root AP to protect theresource allocated to the relay. When requesting the root AP to protectthe allocated resource, the relay may transfer, to the root AP, a listof the other relay BSSs or the predetermined STAs of the relay BSSs thatseriously interfere with the relay.

The relay AP may inform the root AP of a relay BSS or predetermined STAsinterfering with the relay AP. In addition, each STA in the relay BSSmay inform the relay AP of another relay BSS or predetermined STAs thatseriously interfere with the corresponding STA, and the relay AP maytransmit, to the root AP, information on the other relay BSS and theSTAs that interfere with the STA. In this example, the STA may notrequire a measurement function specified in the 802.11k standards, andthe like.

In a case in which STAs have the measurement function, the relay AP mayrequest the STAs to perform a measurement, and identify another relayBSS or STA that interferes with an STA associated with the relay AP,based on a result of the measurement received from each STA. The relayAP may notify the identified relay BSS and the STA to the root AP.

In response to a resource protection request received from a relay, theroot AP may indicate a relay BSS or predetermined STAs of the relay BSSstrictly disallowed to perform transmission in a DRAW for the relayrequesting the resource protection.

When the relay is included in a list of relays prohibited fromperforming transmission in a DRAW allocated to another relay BSS, therelay may not perform transmission in the transmission duration for theother relay BSS. The relay may explicitly prohibit transmission of anSTA by allocating an empty RAW or AP PM RAW to the STA belonging to therelay, thereby protecting the resource of the relay. When in the DRAW isindicated that transmission with respect to a portion of STAs in a relayBSS, rather than the entire relay BSS, is prohibited, the relay mayprohibit the predetermined designated STAs from performing transmissionin the transmission duration of the corresponding relay BSS.

To prohibit transmission of a predetermined STA in the relay BSS, amethod (1) using a modified AP PM RAW or a modified empty RAW, or amethod (2) using RAW allocation may be employed. In the method (1), arelay may include, in the AP PM RAW or the empty RAW, an AID or partialAID list of STAs to be prohibited from performing transmission in apredetermined duration. The relay may explicitly disallow a prohibitedSTA to perform transmission in an AP PM RAW duration or an empty RAWduration, and allow remaining STAs to perform transmission throughcontention. In the method (2), the relay may disallow an explicitlyprohibited STA to perform transmission by not allocating the prohibitedSTA to a RAW. The prohibited STA may correspond to an STA affected byinterference of another relay.

In a case in which the relay is affected by interference of apredetermined STA in the root BSS and requests resource protection, thecorresponding STA may not be included in a DRAW, and the root AP mayprohibit the corresponding STA from performing transmission for therelay transmission duration.

When a DRAW is used, fields may be added to the DRAW, and a strictlydisallow bit, and a list of relay APs and STAs may be indicated in thefields.

In a case in which information related to a strictly disallowed STA isindicated in the DRAW, a length of a beacon may overly increase. Asanother method, the root AP may collect information related to a relayAP and an STA to be strictly disallowed. The information related to therelay AP and the STA to be strictly disallowed may be received from therelay. The root AP may broadcast or unicast, to each relay using aseparate frame, a message including the information related to the relayAP and the STA to be strictly disallowed for each relay BSS. The relayreceiving the message may verify whether the relay or an STA associatedwith the relay is strictly disallowed in a transmission duration ofanother relay. When it is verified that the relay or the STA associatedwith the relay is strictly disallowed, the relay may not performtransmission in the transmission duration of the other relay.

A DRAW may be allocated periodically. In this example, a PRAW may beused. Since a relay beacon may be transmitted periodically at a point intime at which or before the DRAW starts, use of the PRAW may besuitable.

A transmission interval of the relay beacon may be determined through anegotiation between the relay and the root AP when the relay isassociated with the root AP. The transmission interval of the relaybeacon may be identical to a root AP beacon interval or a multiple ofthe root AP beacon interval.

The relay may receive the root beacon and verify whether a DRAW isallocated to the relay. In a case in which the DRAW is allocated to therelay, the relay may allocate a RAW/slot for transmission with STAsassociated with the relay within a duration range allocated to the DRAW.The relay may verify, based on a TIM of the root beacon, whether theSTAs associated with the relay include DL data. When DL data is receivedfrom the root AP, the relay may schedule DL transmission for an STA.When the relay transmits a relay beacon to an STA, the relay may informthe STA of RAW/slot allocation information and information regardingwhich STA includes DL data, through a TIM of the relay beacon. An STAassociated with the relay may not confirm the root beacon, but mayconfirm the beacon of the relay which the STA is associated with.

The relay may receive a PS-Poll from an STA by enabling a PS-Poll RAW tobe allocated immediately after the relay beacon is transmitted. Inaddition, the relay may receive UDI information from the STA andtransmit a resource allocation frame, thereby adjusting initial RAW/slotallocation performed when the relay transmits the relay beacon.

The relay may utilize a DRAW allocated to the relay to be suitable fortransmission with an STA associated with the relay through properRAW/slot allocation. In this example, standards identical to those forgeneral RAW/slot allocation may be used in a method of allocating aRAW/slot within the DRAW.

In a case in which an STA transmits data in a duration other than a DRAWin which transmission between the relay and the STA is guaranteed by theroot AP, a collision with transmission of an STA associated with anotherrelay or transmission between the relay and the root AP may occur. Therelay may disallow STAs associated with the relay to performtransmission in the duration other than the DRAW duration allocated tothe relay, thereby preventing collisions in the BSS. In this example,transmission of an STA may be allowed in a duration in which thetransmission of the STA is explicitly allowed, and may be disallowed inremaining durations, in RAW/slot allocation of the DRAW. In an example,1 bit may be used to indicate whether transmission is to be prohibitedin durations other than the DRAW duration in which the transmission ofthe STA is allowed.

As another method, among durations other than a DRAW, a duration inwhich STAs associated with the relay are strictly disallowed to performtransmission may be explicitly allocated as a RAW, and prohibition ofthe transmission may be informed through the RAW. Such a RAW may bereferred as an empty RAW at a level 1. All durations other than the DRAWmay be allocated as empty RAWs, or a duration in which an STA isstrictly disallowed to perform transmission, among the durations otherthan the DRAW, may be allocated as an empty RAW. In an example, 1 bitthat indicates whether a RAW corresponds to an empty RAW, for example, aRAW in which transmission is prohibited, may be allocated to the RAW. Astart point at which transmission is disallowed and a duration in whichtransmission is disallowed may be signaled by a start time and aduration of the RAW.

In a duration, corresponding to an empty RAW, in which transmission isnot explicitly prohibited, an STA belonging to the relay may performtransmission as an exception in a duration in which transmission beingperformed in another relay BSS is not sensed, or in a duration in whicha RAW is not allocated within a duration allocated for transmission inthe other relay BSS when a beacon of the corresponding relay isreceived.

As still another method, STAs belonging to the relay may performtransmission through contention, similar to transmission in aconventional OBSS environment, even in a duration in which transmissionof the STAs to an AP is not allowed. Since a probability of collisionsmay be relatively high in a case in which transmission is performed in aduration not allocated to a BSS which an STA belongs to, the STA mayperform RTS/CTS in advance of data transmission.

The relay or the root AP may explicitly prohibit transmission of STAsassociated with the relay or the root AP by setting, as an empty RAW, aduration in which intense contention or collisions are expected, amongtransmission durations not allocated to the relay or the root AP.

In addition, the relay AP may prohibit an STA in the relay fromperforming transmission to the relay by allocating, as an empty RAW, aduration in which transmission between the relay and the root AP isperformed.

The relay may sleep for power saving in a duration in which transmissionbetween the relay and the root AP is not performed, among durations inwhich transmission of an STA associated with the relay is prohibited. Inaddition, the root AP may sleep for power saving in a duration in whichtransmission with an STA or a relay directly associated with the root APis not performed, among DRAW durations. The relay may wake for a DRAWduration allocated to the relay.

FIG. 24 illustrates an example of a leveled slot allocation method usinga DRAW according to an embodiment.

Referring to FIG. 24, a DRAW at a level 0 may be disposed to be adjacentto a DL RAW and a UL RAW, and DL transmission in an order of a root AP,a relay, and an STA and UL transmission in an order of an STA, a relay,and a root AP may be performed sequentially. In such disposition of theRAW, a transmission delay may be relatively modest since an STA mayreceive DL data and immediately transfer response UL data to the root APconsecutively in a case in which DL transmission from the root AP to thecorresponding STA is performed.

The relay may receive a root beacon, verify whether data transferred bythe relay is present, based on a TIM, and transmit a PS-Poll based on aresult of the verification. The root AP may receive the PS-Poll from therelay, and transmit a resource allocation frame 2410 to optimizeRAW/slot allocation.

The relay may receive a PS-Poll and a UDI from the STA after a relaybeacon is transmitted, and optimize a UL RAW and a DL RAW in a relaytransmission duration corresponding to a DRAW duration allocated by therelay.

The relay may transfer, to the root AP, a size of UL data received fromthe STA in a form of a UDI before transmitting UL data to the root AP,and the root AP may optimize the UL RAW at the level 0 using theresource allocation frame.

FIG. 25 illustrates another example of a leveled slot allocation methodusing a DRAW according to an embodiment.

In FIG. 25, transmission may be performed in an order different from thetransmission order shown in FIG. 24. Referring to FIG. 25, an STA mayreceive DL data from a root AP through a relay. When the STA transmitsUL data to the relay, the relay may transmit the UL data in an UL RAW tobe allocated when a subsequent root beacon is transmitted, or transmitthe UL data in a UL/DL RAW, rather than immediately transmitting the ULdata to the root AP. In this example, the relay may not immediatelytransmit the UL data to the root AP and may store the UL data. When asubsequent root beacon is received and the relay transmits a PS-Poll tothe root AP, the relay may inform the root AP of a size of the UL datareceived from the STA in a previous beacon duration, through a UDI. Theroot AP may optimize the UL/DL RAW for the relay by transmitting asingle PS-Poll RAW and a single resource allocation frame.

The relay may transmit the UDI to the root AP prior to a point in timeat which a subsequent root beacon is transmitted. Since the root AP maybe aware of a size of the UL data from the relay based on the UDIreceived from the relay prior to the point in time at which the rootbeacon is transmitted, the root AP may allocate a UL RAW with anoptimized length from the beginning when the root beacon is transmitted.In this example, a delay may occur in transfer of UL data from the STAto a final destination. Thus, a memory to store the UL data may beneeded.

FIGS. 26 through 28 illustrate examples of a DRAW allocation method in acase in which a leveled slot allocation method is employed according toan embodiment.

FIGS. 26 through 28 illustrate examples of a DRAW allocation method in acase in which the leveled slot allocation method of FIG. 23 is employed,and examples of a DRAW allocation method in a case in which a relaybeacon interval is different from a root beacon interval.

The relay beacon interval may not be identical to the root beaconinterval. A relay may negotiate with the root AP about a relay beaconinterval for transmission of an association request/response frame whenthe relay is associated with the root AP.

Since STAs associated with the relay may have different wake-upintervals, the relay may allocate a RAW at a higher frequency for apredetermined STA group although the same relay beacon interval is used.The root AP may allocate a DRAW to periodically guarantee transmissionwith respect to the STA group. The relay may transmit, to the root AP,information on a type of an STA, a traffic type of the STA, or a wakeup/listen interval along with AID or partial AID information of the STAassociated with the relay, when the relay is associated with the rootAP. The root AP may allocate a DRAW based on the information receivedfrom the relay. In a case in which a service type of an STA associatedwith the relay is changed, or a new STA is associated with the relay,the relay may inform such a change to the root AP.

In FIG. 26, the root beacon interval may correspond to “3”, the relaybeacon interval may correspond to “6”, and a single DRAW for apredetermined relay may be allocated at each root AP beacon interval.The relay may allocate RAWs/slots for STAs based on a DRAW durationallocated to the relay.

In another example, in a case in which a DRAW is allocated periodically,RAW/slot allocation information may be transmitted through a fullbeacon, rather than transmitting the RAW/slot allocation informationthrough each beacon using a PRAW, and a transmission interval of thefull beacon may be designated to be a multiple of a beacon interval, forexample, a short beacon interval.

In a case in which the allocated RAW in the DRAW duration is repeatedperiodically, the relay may provide information related to therepetition of the RAW through a relay beacon using a PRAW.

In FIG. 26, two DRAWs are allocated in the relay beacon interval for therelay. The relay may allocate a transmission duration for an STA thatwakes up more frequently to perform DL/UL transmission to the two DRAWs,and allocate a transmission duration for an STA that wakes up lessfrequently to a single DRAW, among STAs associated with the relay. Forexample, the relay may allocate a transmission duration for an STA sothat a transmission interval for the STA that wakes up more frequentlymay corresponds to “3”, and a transmission interval for the STA thatwakes up less frequently may correspond to “6”.

In FIG. 27, the root beacon interval may correspond to “6”, the relaybeacon interval may correspond to “12”, and two DRAWs for apredetermined relay may be allocated at each root beacon interval. Theexample of FIG. 27 may be suitable for a case in which an STA associatedwith the relay performs transmission more frequently than the rootbeacon interval. A DRAW 1 and a DRAW 2 may be allocated to thepredetermined relay, and the STA may perform transmission at an intervalshorter than the root beacon interval.

In FIG. 28, the DRAW 1 and the DRAW 2 of FIG. 27 may be allocated todifferent relays. The root beacon interval may correspond to “6”, eachrelay beacon interval may correspond to “6”, and each relay may beallocated a DRAW at an interval of “6”.

FIG. 29 illustrates an example of allocating a frequency subband to arelay according to an embodiment. For example, FIG. 29 illustrates anexample of sharing a RAW between relay clusters, each corresponding to agroup of a relay and STAs associated with the relay.

When transmission between the relay clusters is separable, a durationallocated as an empty slot or an empty RAW at a level 0 in a leveledslot allocation method may be shared between the relay clusters, andsimultaneous transmission between the clusters may be enabled. Forexample, RAW sharing may be enabled (1) when different frequencysubbands are used, or (2) when clusters are spatially separated, or whena few number of STAs are included in a single relay group andtransmission is performable in a chronological order by allocating theSTAs to a single RAW.

<1. Method of Performing RAW Sharing Using Different Frequency Subbands>

A root AP may allocate a channel to be used for transmission betweeneach relay and an STA. The relay may inform the root AP of a channelrange preferred by the relay when the relay is associated with the rootAP. The root AP may allocate, to a relay to be newly associated with, achannel to be used for transmission between the relay and the STA basedon a channel occupation state of other relays in a BSS.

The same primary channel may be used for transmission between the rootAP and the relay. Each relay may use a channel different from theprimary channel of the root AP for transmission with an STA associatedwith the corresponding relay.

The root AP may allocate relays using non-overlapping channels in acluster to the same DRAW so that simultaneous transmission betweenclusters may be performed using different frequency subbands. FIG. 29illustrates an example of subband allocation that allocates the relaysusing non-overlapping channels to the same DRAW.

The root AP may inform a transmission allow period and ID information ofa relay allowed to perform transmission for a DRAW through an RPS IE ofa root beacon or a new similar IE. For example, the ID information ofthe relay may include an AID, a partial AID, or a partial basic serviceset identification (BSSID) of the relay. The root AP may transmitinformation on an available channel and information related to the relayto STAs to be newly associated with the root AP or the relay. The rootAP may include a per channel relay allocation bitmap in a beacon, andtransmit the beacon to inform the STAs of whether a channel isavailable. In a case in which a beacon including a per channel relayallocation bitmap is transmitted, an STA attempting to be associatedwith a relay may identify a relay allocated to each channel, based onthe root beacon. The STA may move to a primary channel in which a relayexists, perform scanning, and identify a point in time a beacon of eachrelay is to be transmitted, based on relay RAW allocation information inthe root beacon. In addition, the STA may receive relay beacons fromrelays, and be associated with a relay existing in a predeterminedchannel that the STA prefers. The root AP may indicate, in a beacon or aprobe response, information on a duration until a subsequent relaybeacon is transmitted, a relay beacon interval, and a channel used byeach relay to inform a relay allocation state for each channel. The STAmay determine an optimal relay more quickly based on the relayallocation state for each channel. A shared DRAW may be allocated in aform of a PRAW. An STA associated with a relay may receive a beacon fromthe relay that the STA is associated with.

Transmission between a relay and an STA in each cluster may be performedin a form identical to conventional communication between an STA and anAP in an independent BSS. An STA in a cluster may perform transmissionwithin a channel range allocated to be used by a relay that the STA isassociated with in the cluster. The STA may perform transmission withina channel range including a primary channel in a cluster designated by arelay. A relay may inform STAs of a primary channel to be used in acluster of the corresponding relay through a relay beacon using the samemethod in which a conventional AP informs STAs of a primary channel of aBSS through a beacon.

In a case in which a RAW is shared using a frequency subband, a root APmay delegate use of each channel to an AP using a DRAW. The AP mayallocate a detailed RAW/slot of the DRAW. In relation to the DRAWallocation, in a case in which a primary channel used by the root AP fortransmission with an STA directly associated with a relay or a root APis not allocated to another relay, the root AP may delegate the primarychannel of the corresponding DRAW to the root AP. The root AP mayallocate a detailed RAW/slot for an STA or a relay that performstransmission directly with the root AP, based on the DRAW allocated tothe root AP. In this example, the root beacon may include DRAWallocation information and RAW/slot allocation information between theroot AP and the relay or the STA with respect to the DRAW durationallocated to the root AP.

In a case in which the relay desires to switch a channel to be used in acluster of the relay, the relay may request the root AP to switch thechannel to be used in the cluster of the relay. For example, the relaymay request the root AP to switch the channel by defining a relayoperating module notification frame. The root AP receiving a channelswitching request from the relay may transfer an acknowledgement of thechannel switching request to the relay, and the relay may move toanother channel in a case in which the root AP approves channelswitching. In a case in which the relay switches the channel, the rootAP may change relay grouping. In a case in which channel switching in acluster is allowed, information on the channel switching may betransferred to an STA through a conventional channel switchannouncement.

FIG. 30 illustrates a case in which frequency selective transmission(FST) is used in a cluster when a subband for a relay is allocatedaccording to an embodiment.

A primary channel in a cluster, for example, a primary channel to beused for transmission between a relay and an STA, may be allocated to befixed. However, the FST may be applied to the cluster such that atemporary primary channel may be changed for each RAW. FIG. 30illustrates an example of allocating a frequency subband to a relay. Incontrast to FIG. 29, a primary channel in a cluster may not be fixed,and the primary channel may be changed for each RAW within a range of aband allocated to the cluster.

FIG. 31 illustrates an example of sharing a RAW using differentfrequency subbands according to an embodiment.

In FIG. 31, the leveled slot allocation method of FIG. 23 may beextended to a method of performing simultaneous transmission by sharinga DRAW using different frequency subbands. Various forms of DRAWallocation methods described with reference to FIGS. 26 through 28 maybe extended to simultaneous transmission using different frequencysubbands.

FIG. 32 illustrates an example of transmitting data using differentfrequency subbands according to an embodiment.

In FIG. 32, the general leveled slot allocation method of FIG. 17 may beextended to a case in which there are two relays that communicate withan STA using different frequency subbands.

In a DL RAW in which transmission is performed from a root AP to a relayat a level 0, and a UL RAW in which transmission is performed from arelay to a root AP at a level 0, transmission slots for a relay 1 and arelay 2 may be allocated sequentially, and a root beacon including slotallocation information may be transmitted.

A DL and UL RAW for transmission between the relay 1 and an STA andtransmission between the relay 2 and an STA may be indicated in the rootbeacon in a form of an empty RAW. The empty RAW may correspond to aDRAW. In this example, information related to a relay allowed to performtransmission in the corresponding empty RAW, and channel informationwith respect to a frequency subband allocated to each relay may beindicated in the empty RAW of the root beacon. For example, theinformation related to the relay allowed to perform transmission mayinclude an AID, a partial AID, a BSSID, or a partial BSSID of each ofthe relay 1 and the relay 2. The channel information may includeinformation on a channel number with respect to a frequency subbandallocated to each relay, whether transmission in a wideband includingthe allocated frequency subband is allowed, and a range of a wideband tobe used when wideband transmission is allowed. The information on therange of the wideband to be used may be used to prevent relays fromusing overlapping channels.

Each relay may allocate a transmission slot for an STA associated withthe corresponding relay to a relay beacon.

In FIG. 32, simultaneous transmission may be performed in the DL and ULRAW duration, for example, a shared RAW, since the relay 1 and the relay2 use different frequency subbands.

Each relay may allocate a UL duration and a DL duration in the sharedRAW differently as necessary. For example, in a case in which the relay1 performs UL transmission from an STA more frequently than the relay 2,the relay 1 may be allocated more UL slots than the relay 2.

The root AP may negotiate with each relay about a preferred frequencysubband, and whether RAW sharing using a frequency subband is to be usedwhen the corresponding relay is associated with the root AP. Inaddition, even after the relay is associated with the root AP, the rootAP may change whether the RAW sharing is to be used, and the preferredfrequency subband through an operating mode change request/responsebetween the relay and the root AP.

The root AP may allocate the same channel to a predetermined relay foreach relay transmission duration, or may determine an optimal channelfor each relay transmission duration and allocate the determined optimalchannel to the corresponding relay transmission duration.

The root AP may allocate a frequency subband so that the relay may use apredetermined frequency subband, for example, 2 megahertz (MHz). Theroot AP may allow the relay to use a wider frequency subband, forexample, 8 MHz, including the allocated predetermined frequency subband.

In a case in which the root AP allows the relay to use a wider frequencysubband, there may be a risk that relays sharing a RAW may useoverlapping frequency subbands. To prevent such a risk, the root AP mayset selectable channel numbers, and restrictions on a bandwidth.

By enabling simultaneous transmission between different clusters asdescribed above, a transmission efficiency may increase.

FIG. 33 illustrates an example of a method of sharing a RAW usingdifferent frequency subbands in a leveled slot allocation method usingan empty slot according to an embodiment.

FIG. 33 illustrates an example extended from the example of FIG. 18.Areas 3310 may correspond to durations in which simultaneoustransmission between clusters is possible.

A DL slot allocated for a RAW 2′ and a UL slot allocated for a RAW 3′may be indicated in a root beacon in a form of empty slots. In thisexample, information related to a relay allowed to perform transmissionin the corresponding empty slot, and channel information with respect toa frequency subband allocated to each relay may be indicated in the rootbeacon. For example, the information related to the relay allowed toperform transmission may include an AID, a partial AID, a BSSID, or apartial BSSID of each of a relay 1 and a relay 2. The channelinformation may include information on a channel number with respect toa frequency subband allocated to each relay, whether transmission in awideband including the allocated frequency subband is allowed, and arange of a wideband to be used when wideband transmission is allowed.The information on the range of the wideband to be used may be used toprevent relays from using overlapping channels.

In a case in which a frequency sub-channel used by a relay is changedfor each relay transmission duration, the relay may transmit a soundingframe for each channel immediately after a relay beacon is transmitted.Each STA associated with the relay may search for an optimal channelbased on the sounding frame, and the relay may transmit data using theoptimal channel selected by the corresponding STA, whereby atransmission efficiency may increase.

FIGS. 34 and 35 illustrate other examples of a method of sharing a RAWusing different frequency subbands in a leveled slot allocation methodusing an empty slot according to an embodiment.

FIG. 34 illustrates an example extended from the example of FIG. 19. Ashared DL RAW and a shared UL RAW may be allocated as a single sharedRAW, for example, a UL/DL RAW. FIG. 35 illustrates an example extendedfrom the example of FIG. 20. A DL RAW and a UL RAW may be shared fortransmission between a relay 1 and an STA and transmission between arelay 2 and an STA.

FIG. 36 illustrates still another example of a method of sharing a RAWusing different frequency subbands in a leveled slot allocation methodusing an empty slot according to an embodiment.

FIG. 36 illustrates an example extended from the example of FIG. 21. ADL RAW and a UL RAW may be allocated as a single shared RAW, forexample, a DL/UL RAW, for transmission between a relay 1 and an STA andtransmission between a relay 2 and an STA. By allocating the DL/UL RAWas a single RAW, a UL slot and a DL slot between the STA and the relay 1and between the STA and the relay 2 may be flexibly allocated dependingon a situation, whereby the RAW may be utilized more efficiently. InFIG. 36, since the relay 1 performs UL transmission from an STA morefrequently than the relay 2, more UL slots may be allocated to the relay1.

<1.1 Signaling Method in a Case of RAW Sharing Using a FrequencySubband>

In the case of RAW sharing using a frequency subband, a root AP mayinform a relay of information on an AP allocated a transmissionduration, a length of the transmission duration, a frequency used in aparticular time duration, for example, a particular RAW or a particularslot, through signaling.

The root AP may transmit, to the relay, information on a transmissionallow period and information related to a relay allowed to performtransmission for a DRAW using an RPS IE of a root beacon or a new IEsimilar to the RPS IE. The information related to the allowed relay mayinclude information on an AID, a partial AID, or a partial BSSID of therelay.

For example, the signaling method may be performed based on Table 1.Table 1 shows DRAW signaling (signaled in root beacon—for level 0).

The root beacon may include DRAW allocation information.

In the information listed in Table 1, RAW start time and RAW durationinformation of a conventional RPS IE may be used, DRAW indication andDRAW allocation information may be added to the RPS IE, or a new IEcontaining similar information may be defined.

TABLE 1 Feature Value Interpretation DRAW indication 1 bit describeswhether RAW corresponds to Delegated RAW. DRAW Start 8 bits describespoint in time at which DRAW starts. Field present Time in conventionalRPS IE may be used. In this example, DRAW Start Time is defined asDuration in TU from end of beacon transmission to DRAW Start time. DRAWDuration TBD(To Be describes the length of DRAW. Field present inDetermined) conventional RPS IE may be used. In this example, the bitsDRAW Duration is defined as Duration of DRAW in TU. DRAW allocation TBDbits describes list of AIDs or partial AIDs or BSSIDs or Partial BSSIDsof relays allowed to perform simultaneous transmission in thecorresponding DRAW. Strictly disallow 1 bit describes whethertransmission of predetermined relay or STAs is to be explicitlyprohibited in allocated duration. List of Relay BSS TBD bit describesstrictly disallowed relay or BSS in relay. and STAs lists single Relay(Partial AID) + disallowed STA (partial) (multiple) AID list in thecorresponding relay. Multiple Relay AID lists may be provided. (Whentransmission of the entire Relay BSS is disallowed, STA (Partial) AIDmay be omitted, or indicated using predetermined pattern, for example,000..0 or 111.11)

The relay and the root AP may be aware of channel information to be usedby each relay. The channel information to be used by each relay may benegotiated with the root AP. Thus, the root AP may not provideinformation regarding which channel is allocated to be used by whichrelay in each DRAW, in DRAW units. For example, the negotiated channelinformation may include a channel number in which transmission for apredetermined relay is allowed, a bitmap, or information regardingwhether transmission in a wideband including an allocated frequencysubband is allowed. However, in a case in which information on anavailable channel and information related to the relay are transmittedto STAs to be newly associated with the root AP or the relay, or aduration in which a RAW is yet to be allocated m or a RAW transmissionduration remains, the root AP may transmit a beacon including a perchannel relay allocation bitmap to inform STAs of whether a channel isavailable so that another STA may use the remaining RAW duration.

The root AP may allocate a sub-channel to the root AP when DRAW sharingis used. In this example, an AID, a partial AID, a BSSID, or a partialBSSID of the root AP may be included in DRAW signaling information, andRAW/slot allocation information for transmission between the root AP anda relay or an STA that performs transmission directly to the root AP maybe included in a root beacon.

In a case in which a form of a PRAW is used, 1 bit indicating whether aRAW corresponds to a PRAW, and information on an interval of the PRAWmay be additionally included in the root beacon. For example, theinterval of the PRAW may correspond to an integer value that indicates amultiple of a short beacon. 1 bit indicating whether a RAW correspondsto a PRAW may be omitted, and information on the interval of the PRAWmay be additionally included in the root beacon in addition to the itemslisted in Table 1.

DRAW signaling in a case in which DRAW sharing is not used may beperformed in the same manner as the method described above, except adifference that a single relay allowed to perform transmission may bedesignated in DRAW allocation.

A strictly disallowed bit may indicate whether transmission of apredetermined relay or STAs is to be explicitly prohibited in anallocated duration. When the strictly disallowed bit corresponds to “1”,information related to a strictly disallowed relay and a strictlydisallowed STA may be included in a DRAW. Whether the entire relay BSSis disallowed or whether a portion of STAs in the relay BSS isdisallowed may be indicated using the strictly disallowed bit.

Table 2 lists empty RAW signaling information included in a relaybeacon.

TABLE 2 Feature Value Interpretation Empty RAW 1 bit describes whetherRAW corresponds indication to Empty RAW. Empty RAW 8 bits describespoint in time at which Empty Start Time RAW starts. Field present inconventional RPS IE may be used. In this example, Empty RAW Start Timeis defined as Duration in TU from end of beacon transmission to EmptyRAW Start time. Empty RAW TBD bits describes length of Empty RAW. Fieldpresent Duration in conventional RPS IE may be used. In this example,Empty RAW Duration is defined as Duration of Empty RAW in TU.

The empty RAW may indicate a duration in which transmission of an STA ina cluster is prohibited outside the DRAW duration at a level 1. When aRAW is indicated as an empty RAW, an STA in the cluster may beprohibited from transmitting data during a duration specified as a RAWstart time and RAW duration.

As another example, a duration in which an AP enters a power save modemay be explicitly indicated. When an AP power save bit is set to “1” inan RPS IE, the AP may sleep in the corresponding RAW duration, and anSTA may not transmit data to the AP. Empty RAW signaling may beperformed using the AP power save bit. When a duration to be set as anempty RAW is set as a RAW, and the AP power save bit is set to “1”, STAsmay not perform transmission in the DRAW or RAW duration.

Conversely, the AP power save mode may be explicitly indicated using theempty RAW signaling method. When a duration in which the AP performspower saving is set as an empty RAW, an STA may not perform transmissionin the duration set as the empty RAW and thus, the AP power save modemay be explicitly indicated. In this example, since a definition of theempty RAW may include a much fewer number of bits than a definition of aconventional RPS IE, a length of the RPS IE may be reduced further in acase in which the empty RAW is applied to an AP power save indication.

As still another example, both an empty RAW indication bit and an APpower save bit may be indicated in the empty RAW. Although transmissionbetween a relay and an STA associated with the relay is disallowed inthe empty RAW, the relay may perform transmission with the root AP inthe empty RAW and may not perform power saving in reality. Thus, whetherthe relay sleeps in reality may be explicitly indicated using the emptyRAW indication bit and the AP power save bit.

In a case in which the empty RAW is explicitly allocated periodically, aform of a PRAW may be used. In this example, 1 bit indicating whether aRAW corresponds to a PRAW, and information on an interval of the PRAWmay be additionally included in a root beacon. For example, the intervalof the PRAW may correspond to an integer value that indicates a multipleof a short beacon. 1 bit indicating whether a RAW corresponds to a PRAWmay be omitted, and information on the interval of the PRAW may beadditionally included in the root beacon in addition to the items listedin Table 1.

In a case in which transmission of an STA in a cluster is explicitlyprohibited outside the DRAW, the empty RAW may not be used, and therelay may allocate 1 bit in a relay beacon and indicate whethertransmission is prohibited in durations other than the DRAW or RAWduration explicitly allocated by the relay. For example, when theallocated bit corresponds to “1”, an STA may not perform transmission indurations other than the duration in which the RAW or the DRAW isexplicitly set.

As another example, a duration in which an AP enters a power save modemay be explicitly indicated. When an AP power save bit is set to “1” ina short beacon or a beacon, an STA may be prohibited from performingtransmission to the AP in durations other than the explicitly allocatedRAW duration. Whether transmission in durations other than the DRAW orRAW duration for the relay is prohibited may be indicated using the APpower save bit. In a case in which the transmission in durations otherthan the DRAW or RAW duration for the relay is explicitly prohibited,STAs may not perform transmission in the DRAW or RAW duration when theAP power save bit is set to “1” in a relay beacon.

RAW information allocated by a relay to an STA at a level 1 may besimilar to RAW information in the conventional 802.11ah standards. In acase in which FST is used in a cluster, primary channel information forFST may be included in an RPS IE of a relay beacon, similar to theconventional 802.11ah standards.

In addition, modified examples, for example, Option 1 and Option 2, maybe possible. In the following description, an empty slot or an empty RAWat a level 0 may refer to a delegated slot or DRAW.

<Option 1—Example of a Case in which Empty Slot is Used>

In a case in which an empty slot is used, information as follows may beincluded in an RPS IE.

1) RAW start time: RAW start time indicates a start time of a RAWincluding a shared empty slot.

2) RAW duration: RAW duration indicates a duration of a RAW including ashared empty slot.

3) Empty (delegated) slot definition: Empty slot definition may indicatea start point and an end point of an empty slot. For example, the emptyslot definition may include a start slot number, and an end slot number.In a case in which a number of empty slot groups are present in the sameRAW, a list of start points and end points of the empty slots may becompiled. In a case in which the empty slot definition indicates that aroot AP uses an empty slot, an empty slot allocation field may bepresent, and transmission between a relay AP and an STA associated withthe corresponding relay indicated in the empty slot allocation field maybe allowed in a shared empty slot. When the relay AP sets an empty slotdefinition field, the empty slot allocation field may be unnecessary,which may indicate that transmission between the relay AP and the rootAP may be allowed. An empty RAW indication at a level 1 may be used in acase in which transmission of an STA is explicitly prohibited.

4) Empty (delegated) slot allocation: Empty slot allocation may be usedfor a DL/UL allocation frame or an RPS IE of a root AP. The empty slotallocation may include a list of relay APs allowed to performtransmission with associated STAs in an empty slot, and information on afrequency subband available to a relay AP. The subband information maybe included in a case in which RAW sharing using frequency subbands isused. In a case in which simultaneous transmission between spatiallyseparated clusters or RAW sharing in a time domain is performed, thefrequency subband information may not be included. The root AP and arelay may share the frequency subband information beforehand, or mayenable a band allocation map to be included in a root beacon and preventband allocation information from being included in the root beacon. Forexample, the list of the allowed relay APs may include information onAIDs, partial AIDs, BSSIDs, and partial BSSIDs of the allowed relay APs.The frequency subband information may include a channel number in whichtransmission is allowed, a bitmap, or whether transmission in a widebandincluding an allocated frequency subband is allowed. In a case in whichtransmission using a frequency subband wider than a selected frequencysubband is allowed, the root AP may prevent a channel from being usedrepeatedly between relays by indicating, using a bitmap, a bandwidth ora channel allowed to be used.

In addition to the information mentioned above, information on slotdefinition, group/resource allocation frame indication, and accessrestricted to paged STA only may be included in the RPS IE.

<Option 2—Example of a Case in which Empty RAW (DRAW) is Used>

In a case in which an empty RAW (DRAW) is used, information as followsmay be included in an RPS IE:

1) RAW start time: RAW start time indicates a start time of a sharedRAW.

2) RAW duration: RAW duration indicates a duration of a shared RAW.

3) Empty RAW (DRAW) indication: Empty RAW indicates whether a RAW isused as an empty RAW. In a case in which the empty RAW indicationindicates that a root AP uses an empty RAW, an empty RAW allocationfield needs to be present and only transmission between relay APsindicated in the empty RAW allocation field and STAs associated with thecorresponding relay APs may be allowed in a shared empty RAW. When arelay AP sets the empty RAW indication field, the empty RAW allocationfield may be unnecessary, which may indicate that transmission betweenthe relay AP and the root AP is allowed. Only in a case in whichtransmission of an STA is explicitly prohibited, an empty RAW indicationat a level 1 may be used.

4) Empty RAW (DRAW) allocation: Empty RAW allocation may be used onlyfor an RPS IE of a root AP. The empty RAW allocation may include a listof relay APs allowed to perform transmission with associated STAs in anempty RAW, and frequency subband information on a frequency subbandavailable to a relay AP. The frequency subband information may beincluded only in a case in which RAW sharing using frequency subbands isperformed. In a case in which simultaneous transmission betweenspatially separated clusters or RAW sharing in a time domain isperformed, the frequency subband information may not be included. Forexample, the list of the allowed relay APs may include information onAIDs, partial AIDs, BSSIDs, and partial BSSIDs of the allowed relay APs.The frequency subband information may include a channel number in whichtransmission is allowed, a bitmap, or whether transmission in a widebandincluding an allocated frequency subband is allowed. The root AP and arelay may share in advance frequency subband information. Alternatively,a band allocation map may be included in a root beacon and bandallocation information may not be included therein. In a case in whichtransmission using a frequency subband wider than a selected frequencysubband is allowed, the root AP may prevent a channel from being usedrepeatedly between relays by indicating, using a bitmap, a bandwidth ora channel allowed to be used.

<2. Method of Performing RAW Sharing in a Case in which Clusters areSpatially Separated>

FIG. 37 illustrates an example of a method of performing RAW sharing ina case in which clusters are spatially separated according to anembodiment. The embodiment of FIG. 37 is an example of a case in whichan empty RAW is used, and may be extended using a similar methodalthough an empty slot is used. Areas 3310 indicate durations in whichclusters are spatially separated and simultaneous transmission betweenthe clusters is possible. A signaling method is similar to a signalingmethod used when performing RAW sharing using a frequency subband.

<3. Method of Performing RAW Sharing Using Time Domain>

FIG. 38 illustrates an example of a method of performing RAW sharingusing a time domain according to an embodiment. The embodiment of FIG.38 is an example of a case in which an empty RAW is used, and may beextended using a similar method although an empty slot is used. Areas3410 indicate durations in which a RAW is shared by performingsequential transmission in the time domain.

In a shared RAW or slot, a relay or an STA may perform sequentialtransmission through contention. The method of performing RAW sharingusing a time domain may be used when the number of STAs associated witheach relay is relatively small or when a transmission amount isrelatively small. A signaling method is similar to a signaling methodused when performing RAW sharing using a frequency subband.

Another method that may be considered in a DRAW transmission method is amethod in which a root AP does not set a DRAW as a duration fortransmission within a relay BSS and a relay allocates, as the DRAW, aduration including an UL/DL transmission duration of the root AP. In acase in which the above method is used, the relay may directly andappropriately allocate a RAW/slot with respect to level-1 transmissionwithin the relay and transmission from the relay to the root AP withinthe DRAW.

A UL/DL transmission RAW/slot from a relay to a root AP may be indicatedin a relay beacon. A transmission slot indication to the root AP may beindicated in an RPS IE using a method similar to a method used for anSTA belonging to a relay BSS. For example, in a case of slot allocation,an AID of the root AP may be indicated for transmission from the relayto the root AP, and UL/DL transmission to the root AP may be indicatedas DL/UL transmission with respect to an AID of the corresponding rootAP in an RPS IE.

<(B) Method in which a Root AP Independently Allocates Resources, forExample, a Relay Transmission Duration and a Relay Transmission Band, toa Relay Using Separate Resource Allocation Information Instead of Usinga RAW Form (Method Using a Relay Resource Allocation IE)>

In the method (A) using a DRAW, a root AP allocates a duration set in aRAW form to a relay and thus, an existing RAW signaling method may besimply extended and used. Also, empty RAW signaling for transmissionduration protection may be simultaneously performed together withresource allocation through a DRAW. In a case in which relays use achannel different from the root AP, each of the relays may performtransmission in a frequency subband allocated thereto independently fromthe root AP and thus, there is no need to determine a relay transmissionduration based on a RAW of the root AP. In the method (B), a root AP mayallocate a resource to the relay using separate resource allocationinformation, which is independent from RAW allocation of the root AP.Accordingly, the relay and the root AP present in different frequencysubbands may perform transmission in independent durations.

Hereinafter, a general case in which a plurality of frequency subbandsis used will be described, which includes a case of a single band.

A root AP may include, in a root beacon, resource allocation informationrequired for transmission between a relay and an STA in a form of aseparate resource allocation IE and thereby transmit the root beacon. Ina case of a relay operation also using multi-band transmission, the rootAP may allocate a resource to each relay in order to minimizetransmission of a different relay cluster in the same frequency subbandat a predetermined time. To enable simultaneous transmission, the rootAP may allocate a resource so that different relays may performtransmission within a cluster using different frequency subbands at apredetermined time.

A resource to be allocated may include a transmission allow start timeand a transmission duration length for transmission within a cluster ofeach relay and channel information to be used by each relay in a case inwhich each relay is to use transmission within a cluster.

Once a relay is associated with a root AP as an STA, the relay mayrequest the root AP to set up a relay BSS and operate as a relay AP, andmay operate as the relay AP in response to an approval from the root AP.

When a relay requests association to a root AP as an STA, or when therelay requests the root AP to operate as the relay AP, the relay maytransfer, to the root AP, resource allocation requirements, for example,channel related information such as a channel and a bandwidth to be usedby the relay for cluster transmission and primary channel information, arelay beacon interval, and an initial relay BSS transmission duration.The relay may also transmit, to the root AP, information on a separationlevel with respect to another relay BSS together with the resourceallocation requirements. The relay may operate as the relay AP bysetting up the relay BSS using a relay beacon interval and a channelallocated by the root AP, and by transmitting a relay beacon at apredetermined time. The relay may transmit, to the root AP, informationused to determine a required transmission time when the relay isassociated with the root AP, when the relay requests the root AP tooperate as the relay AP, or thereafter. For example, the relay maytransmit, to the root AP, information, for example, a mean data rate ofSTAs associated with the relay, a target wake time, or a wake interval.The root AP may allocate an appropriate transmission duration to therelay based on information received from the relay. The root AP may alsoallocate the same transmission duration to spatially separated relaysbased on information on a separation level with respect to another relayBSS that is received from the relay. Also, the relay AP may periodicallyor aperiodically measure a degree of spatial separation with the otherrelay BSS, and may feedback modified contents to the root AP when thedegree of spatial separation with the other relay BSS is modified by apredetermined reference or more. For example, when the relay AP isaffected by great interference of existing separated another relay BSS,the relay AP may inform the root AP of the above situation.Alternatively, when a new relay BSS is detected, the relay AP may informthe root AP of the detected new relay BSS. Additionally, the root AP mayallocate the same duration for transmission of the spatially separatedrelays, based on spatial separation information between the relays.

A relay and a root AP may be mutually aware of channel allocationinformation on the relay. To minimize a length of resource allocationinformation to be transferred for each beacon, channel allocationinformation on each relay may be transmitted without being included inthe resource allocation information. Channel information allocated toeach relay may be included in resource allocation information to betransferred for each beacon. Each of the relays may identify channelallocation information of different relays based on a root beacon, andmay verify a relay allocated to the same channel as a channel of acorresponding relay.

When the same resource is allocated for each (short) beacon duration,interval information associated with resource allocation may be includedin, for example, a long beacon and thereby transmitted, instead oftransmitting resource allocation information for each beacon duration.In this example, only when resource allocation is modified, modifiedresource allocation information may be transmitted.

A root AP may include resource allocation information in a root beaconand thereby transmit the same. A relay may allocate a RAW for atransmission time in which transmission to a cluster is allowed, basedon resource allocation information included in the root beacon. Therelay may include RAW allocation information on an STA in a relay beaconand then transmit the same to STAs associated with the relay.Transmission between the relay and an STA may be performed within anallocated resource. The relay may use a channel allocated through anadvance-negotiation with the root AP for a relay beacon transmissionchannel and a channel used for transmission with an STA within acluster. Channel allocation information may be indicated using relayresource allocation information, or may be omitted. A channel allocatedby the root AP may be used for transmission between the relay and theroot AP. The transmission between the relay and the root AP may beperformed based on a transmission duration allocated by the root AP to aroot beacon as a RAW.

The same leveled method as the method (A) may be employed for the abovemethod. That is, a root AP may allocate only a resource for a relaycluster, and may not allocate a RAW of an STA associated with a relaywithin the relay cluster. The root AP may allocate only a RAW for arelay and an STA directly associated with the root AP. RAW allocationwith respect to an STA associated with each relay may be performedwithin a resource allocated to a corresponding relay, for example, atransmission channel and a transmission duration allocated to thecorresponding relay.

An STA associated with a relay may verify RAW/slot allocationinformation based on a relay beacon, and a relay and an STA directlyassociated with the root AP may verify the RAW/slot allocationinformation based on a root beacon.

Similar to the method (A), a root AP may set an empty RAW in a rootbeacon to protect transmission of a corresponding relay cluster in acase of transmission between relays using the same frequency subband asthe root AP. That is, the root AP may allocate, as an empty RAW, theentire relay transmission duration using the same frequency subband asthe root AP or a portion thereof. A relay and an STA directly associatedwith the root AP may not perform transmission in a time durationindicated in an empty RAW based on a root beacon. Accordingly, in thetime duration indicated in the empty RAW, transmission of a relaycluster allocated to the same frequency subband as the root AP may beprotected.

A method of setting an empty RAW, which is the same as the method (A),or a method of disallowing transmission excluding transmission of anexplicitly allocated RAW may be used for a protecting method so thatSTAs within each relay cluster may not perform transmission in aduration excluding an explicitly allocated relay cluster transmissionduration.

<Method of Protecting a Resource Allocated to Another Relay>

To prevent a collision of an STA belonging to a root BSS in anotherrelay BSS transmission duration using the same channel, a root AP mayprohibit transmission of the STA by explicitly setting the other relaytransmission duration as an empty RAW or an AP PM RAW. The root AP maydetermine whether the root BSS is spatially separated from the otherrelay BSS. When the root BSS is spatially insufficiently separated, theroot AP may prohibit transmission of an STA associated with the root APin another relay transmission duration by setting the other relaytransmission duration as an empty RAW or an AP PM RAW. Alternatively,the root AP may also prohibit transmission of a predetermined STA thatis greatly affected by interference of the other relay BSS, among STAsin the root BSS, rather than prohibiting transmission of all of the STAsin the root BSS with respect to the other relay transmission duration.To this end, the root AP may use a RAW allocation method of excluding,from RAW allocation, a modified empty RAW or a modified AP PM RAWcapable of indicating an STA prohibited from performing transmission orthe STA prohibited from performing transmission.

A method in which a root AP verifies whether a predetermined STA in aroot BSS is affected by interference of another relay BSS may use amethod in which a root AP receives interference information of an STAusing “(BB) method of determining spatial separation between relays”, oran STA of a root BSS affected by interference directly informs a root APof information on another relay BSS or another STA to which the STAaffects interference.

To prevent a collision occurring when an STA belonging to a relay BSSperforms transmission in a transmission duration of another relay BSSusing the same channel, a relay AP may prohibit transmission by settingthe transmission duration of the other relay BSS as an empty RAW or anAP PM RAW, which is similar to the method (A). A relay may periodicallydetermine whether the relay is spatially separated from another relayBSS. When the spatial separation is determined to be insufficient, therelay may prohibit transmission of an STA associated with the relay bysetting a transmission duration of the other relay as an empty RAW or anAP PM RAW. Alternatively, the relay may prohibit transmission only withrespect to a predetermined STA relatively greatly interfering with theother relay BSS among STAs in the relay BSS. To this end, a RAWallocation method of excluding, from RAW allocation, a modified emptyRAW or a modified AP PM RAW capable of indicating an STA prohibited fromperforming transmission or the STA prohibited from performingtransmission may be used.

In a case in which a frame to be urgently transmitted from a root AP ispresent, transmission in a duration excluding a transmission durationallocated for root BSS transmission may be allowed as an exception.Also, in level-1 transmission, an STA may transmit data, as anexception, in a duration in which transmission being performed inanother relay BSS is not detected, or in a duration which a RAW is notallocated with respect to a corresponding relay BSS as a result of thedetermining based on a beacon of another relay, although the timeduration corresponds to a time duration not allocated to a relay towhich the STA belongs.

Alternatively, even in a duration in which transmission to an AP is notallowed, all of an STA belonging to a root AP and an STA belonging to arelay may be allowed to transmit data through contention, which issimilar to transmission in an existing OBSS environment. However, in acase of transmitting data in a duration that is not allocated to a BSSto which a corresponding STA belongs, a collision probability may berelatively high and thus, the STA may perform RTS/CTS in advance of datatransmission.

A relay or a root AP may explicitly prohibit transmission of STAsassociated therewith by setting, as an empty RAW, a duration in whichintense collision or contention is expected, among transmissiondurations not allocated to the relay or the root AP. In addition, therelay or the root AP may prohibit an STA from performing transmission toa relay in a duration in which transmission between the relay and theroot AP is performed, by setting, as an empty RAW, the duration in whichthe transmission between the relay and the root AP is performed.

The above method of protecting a resource allocated to another relay maybe similarly applicable to the method (A) using a DRAW.

<Protection Method with Respect to a Resource Allocated to a Relay>

A relay may explicitly request a root AP to protect a resource allocatedto the relay. In response to the request from the relay, the root AP mayexplicitly prohibit transmission of predetermined relay BSSs or aportion of STAs of a predetermined BSS with respect to the resourceallocated to the relay, for example, a transmission duration. Here, theportion of STAs may also include an STA of a root BSS.

For example, in a case in which a relay is seriously affected byinterference due to transmission of another relay BSS or predeterminedSTAs belonging to the other relay BSS, or STAs directly associated witha root BSS, and desires to prohibit the entire or a portion of STAs ofthe other relay BSS or the STAs directly associated with the root BSSfrom performing transmission in a transmission duration allocated to therelay, the relay may request the root AP to protect the resourceallocated to the relay. When requesting the root AP to protect theallocated resource, the relay may transmit, to the root AP, a list ofpredetermined STAs or the other relay BSS interfering with the relay.

Also, each of the STAs in a relay BSS may transfer, to a relay AP,information on a predetermined STA or a relay BSS seriously interferingwith a corresponding STA. The relay AP may transfer, to a root AP,information on the relay BSS and the STA transferred from the STA. Inthis example, STAs may not require a measurement function disclosed inthe 802.11k standard and the like. In a case in which STAs have themeasurement function, the relay AP may request the STAs to perform ameasurement and may identify the other relay BSS and the STA thatinterferes with an STA associated with the relay AP based on a result ofthe measurement received from each STA. The relay AP may notify theidentified relay BSS and STA to the root AP.

In response to a resource protection request received from a relay, aroot AP may indicate, in a resource allocation IE, a relay BSS orpredetermined STAs strictly disallowed to perform transmission in acorresponding transmission duration with respect to the relay havingmade the resource protection request.

When a relay is included in a list of relays prohibited from performingtransmission in a resource allocation IE of another relay BSS, the relaymay not perform transmission in a transmission duration of the otherrelay BSS. The relay may explicitly prohibit transmission of an STAbelonging to the relay by allocating an empty RAW or an AP PM RAW to theSTA, thereby protecting a resource of the relay having made a resourceprotection request. When in the relay resource allocation IE isindicated that transmission with respect to a portion of STAs in a relayBSS, rather than the entire relay BSS, is prohibited, the relay mayprohibit only a predetermined STA from performing transmission in thetransmission duration of the corresponding relay BSS. The relay resourceallocation IE may include resource allocation information on a resourceallocated by a root AP and used for transmission between the relay andthe STA associated with the relay. Which relay is communicable with anSTA in which time duration may be determined based on the relay resourceallocation IE.

To prohibit transmission of a predetermined STA in a relay BSS, (1) amethod of modifying and thereby using an AP PM or an empty RAW or (2) amethod using RAW allocation may be employed. In the method (1), a relaymay include, in the AP PM RAW or the empty RAW, an AID or partial AIDlist of STAs to be prohibited from performing transmission in apredetermined duration. The relay may explicitly disallow only aprohibited STA to perform transmission in the AP PM RAW or the empty RAWduration, and may allow remaining STAs to perform transmission throughcontention. In the method (2), the relay may disallow only an explicitlyprohibited STA to perform transmission by not allocating the prohibitedSTA to a RAW. The prohibited STA may correspond to an STA affected byinterference of another relay.

In a case in which a relay is affected by interference of apredetermined STA in a root BSS and requests resource protection, thecorresponding STA may not be included in a relay resource allocation IE,and a root AP may prohibit the corresponding STA from performingtransmission in a relay transmission duration.

The above method of protecting a resource allocated to a relay itselfmay be similarly applicable to the method (A) using a DRAW. In the caseof the method (A), a strictly disallow bit, a list of relay APs, and alist of STAs may be indicated using fields of a DRAW.

In a case in which information even including information a strictlydisallowed STA is indicated in a relay resource allocation IE, a lengthof a beacon may overly increase. As another method, a root AP maycollect information on an STA and a relay AP to be strictly disallowed,which is received from a relay. In this method, the root AP maybroadcast or unicast, to each relay using a separate frame, a messageincluding the collected information for each relay BSS. In response tothe message including information on the STA and the relay AP to bestrictly disallowed, the relay may verify whether the relay itself or anSTA associated with the relay is strictly disallowed in a transmissionduration of another relay. When it is verified that the relay or the STAis strictly disallowed, the relay may not perform transmission in thetransmission duration of the other relay.

<Detailed Description as to Allocation of a Frequency Subband in theMethod (B)>

In an initial stage, a relay attempts to be associated with a root AP asan STA. Next, the relay may request the root AP to set up a relay BSSand to operate as a relay AP, and may operate as the relay AP inresponse to an approval from the root AP.

The relay may request the root AP for a resource required for a clusterof the relay used when the relay operates as the relay AP together withan association request. Alternatively, when the relay requests the rootAP to operate as the relay AP, the relay may also request the root APfor the resource required for the cluster of the relay together with arelay setup request. For example, the relay may include the followinginformation in the association request or the relay setup request andthereby transmit the same to the root AP.

1) Information related to a channel allocation request for a relaycluster: A relay BSS starting channel number, a relay primary channelnumber, and a relay bandwidth may be included in information related toa channel allocation request for a relay cluster. A relay may transmit alist of available channel candidates to a root AP. The root AP mayallocate a channel not overlapping a channel of another relay BSS to therelay. In a case of allocating a plurality of relays to the samefrequency subband, the root AP may allocate relays using the samefrequency subband to different time durations. In a case in which acurrent relay is spatially separated from another relay BSS, the root APmay allocate the same frequency subband to a current relay BSS and theother relay BSS although a time duration corresponds to the same timeduration.

2) Relay beacon interval: A relay beacon interval refers to atransmission interval of a relay beacon. A relay may determine the relaybeacon interval through negotiation with a root AP. The relay mayperiodically transmit a relay beacon subsequent to setup of a relay BSS,and the root AP may allocate, to the corresponding relay, a point intime in which the relay is to transmit a beacon and a predetermined timesubsequent thereto. In a case in which a relay cluster uses the samefrequency subband as the root AP, the root AP may protect a transmissionduration of the relay cluster using an empty RAW.

A relay beacon may be transmitted in a most initial transmissionduration among transmission durations allocated to a relay.Alternatively, a root AP may allocate a relay beacon transmission RAWafter a root beacon is allocated. Each relay may transmit a relay beaconbased on the allocated relay beacon transmission RAW. In this example, atransmission duration allocated to each relay and a point in time inwhich a relay beacon is transmitted may not be directly continued.

In addition, the relay may transmit, to the root AP, requirements suchas a relay transmission duration, for example, a transmission timerequired by a relay during a full beacon interval of the root AP, ortransmission duration related information used when the root APdetermines a relay transmission duration. For example, the transmissionduration related information may include a mean data rate of STAsassociated with the relay, a target wake time, or a wake interval. Theroot AP may allocate a required time duration to each relay clusterbased on the received requirements or transmission duration relatedinformation. In a case of association to the root AP or a relay setuprequest, the relay may transmit relay transmission duration relatedinformation to the root AP. Alternatively, the relay may exchangerelated information with the root AP using an additional resourceallocation request frame after being associated with the root AP. Therelay may also transmit, to the root AP, information on a degree ofspatial separation with respect to another relay BSS.

A root AP may respond to an association request of a relay using anassociation response. Here, information on a transmission durationallocated by the root AP may be included in an association responseframe and thereby be transmitted. Alternatively, in a case in which therelay transfers a relay related parameter to the root AP using aseparate relay setup request, the root AP may include, in a responseframe thereto, information on a transmission duration allocated by theroot AP. For example, the root AP may inform the relay of channelallocation information such as a relay BSS starting channel number, arelay primary channel number, and a relay bandwidth, and a relay beaconinterval allowed by the root AP. Also, the root AP may inform the relayof a negotiation result associated with the relay transmission duration.

Information allocated by a root AP to a relay in an initial stage may bemodified using an additional operation mode change request/responseframe or a resource allocation change request/response frame. When thenumber of STAs associated with a relay increases or decreases, aresource required for transmission of a relay cluster may be changed.The relay may request the root AP for a relay cluster bandwidth andrelay transmission duration requirements even after being associatedwith the root AP. Accordingly, the entire resources may be furtherefficiently utilized. In a case in which a channel used in a relay BSSis changed, the relay AP may notify a channel change to STAs associatedwith the relay AP using a channel switch announcement frame disclosed inan existing 802.11 standard.

The root AP may also allocate the same transmission duration tospatially separated relays based on information on a degree of spatialseparation with respect to another relay BSS, which is transmitted froma relay.

Also, the relay AP may periodically or aperiodically measure a degree ofspatial separation with respect to the other relay BSS. When themeasured degree of spatial separation is greater than or equal to apredetermined reference, the relay AP may feedback modified contents toa root AP. For example, in a case in which the relay AP is affected bygreat interference of existing separated another relay BSS or in anopposite case, the relay AP may inform the root AP of the abovesituation. The root AP may also newly allocate transmission of spatiallyseparated relays to the same duration, based on spatial separationinformation between the relays.

FIG. 39 illustrates an example of allocating a plurality of frequencysubbands according to an embodiment.

For example, FIG. 39 illustrates an example of allocating a plurality ofdifferent frequency subbands to a plurality of relays and a root AP toenable simultaneous transmission. Referring to FIG. 39, transmissionbetween a relay 1 and an STA associated with the relay 1, transmissionbetween a relay 2 and an STA associated with the relay 2, andtransmission between a root AP and a relay or an STA directly associatedwith the root AP may be performed using different channels and thus, maybe simultaneously performed. A relay and a root AP using differentfrequency subbands may independently perform transmission. Relays, forexample, the relay 1 and a relay 3, using the same frequency subband mayneed to perform transmission in different transmission durations. An STAmay communicate with an associated relay using a frequency subband usedby the associated relay. A relay may communicate with a root AP using afrequency subband allocated by the root AP.

FIG. 40 illustrates an example of allocating a plurality of frequencysubbands according to another embodiment.

For example, dissimilar to the example of FIG. 39, FIG. 40 illustrates acase of allocating frequency subbands so that a portion of channels mayoverlap in the example of allocating different frequency subbands to aplurality of relays and a root AP to enable simultaneous transmission.The overlapping channel allocation may be useful in a case in which thenumber of available channels is relatively small. A primary channel ofeach of relay APs and a root AP may not be overlappingly allocated andonly a secondary channel may be overlappingly allocated. In a case inwhich the number of channels is insufficient, the root AP mayoverlappingly allocate a portion of channels as illustrated in FIG. 4,and may transmit, to a relay, channel allocation information on eachrelay that includes even allocation of an overlapping channel. Here, thechannel allocation information is referred to as default channelallocation information. The channel allocation information may be sharedin advance between the relay and the root AP. In addition, channelallocation information may not be explicitly informed using a relayresource allocation IE or may be explicitly informed using the relayresource allocation IE. In a case in which channel allocationinformation is not explicitly informed using the relay resourceallocation IE, the root AP may inform a relay that is allowed to use anoverlappingly allocated channel in a predetermined time duration whentransmitting the resource allocation IE, that is, when performingresource allocation. The root AP may inform, using the resourceallocation IE, information to be additionally informed when performingresource allocation. Information to be additionally informed may includeinformation on an entity that is to use an overlappingly allocatedchannel. When additional channel allocation information is absent in theresource allocation IE, a relay may use a channel allocated to therelay, including the overlappingly allocated channel. When apredetermined relay is allowed to use an overlapping channel, the rootAP may disallow another relay to which the channel is overlappinglyallocated to use the corresponding channel. For example, the root AP maytransfer a reduced bandwidth or a disallowed channel number to the otherrelay to which the channel is overlappingly allocated.

For example, in a case in which a channel CH2 is allocated to both arelay 5 and a relay 3, and a channel CH5 is allocated to the relay 5 ata predetermined point in time, a root AP may inform the relay 3 of abandwidth reduced to be less than an initially allocated bandwidth, ormay inform the relay 5 not to use the channel overlappingly allocated tothe relay 3 using a resource allocation IE. Information on anoverlapping channel allocation may not be included in the resourceallocation IE to be transferred to the relay 5. That is, wheninformation on an overlapping channel allocation is explicitly absent ina resource allocation IE, a relay may use all of the channels allocatedto the relay, including an overlapping channel. Conversely, in a case inwhich channel allocation information is indicated in the resourceallocation IE not to use an overlapping channel or to use a reducedbandwidth excluding the overlapping channel, a relay may performtransmission in a cluster using the reduced bandwidth, that is, thebandwidth excluding the overlapping channel.

Also, in a case in which a transmission amount of a predetermined relayis temporally large and the number of channels is sufficient, a root APmay temporarily allocate, to a corresponding relay, an additionalchannel in addition to an initially allocated channel. The root AP maytransmit information on an extended bandwidth or information on achannel additionally allocated to a resource allocation IE for thecorresponding relay, for example, an additionally allocated channelnumber. In response to the received information on the additionallyallocated channel or information on the extended bandwidth, the relaymay use the channel additionally allocated by the root AP.

Hereinafter, an example of informing allocation of an overlappingchannel or allocation of a temporary additional channel using a resourceallocation IE will be described.

(a) Option 1: indicates using “channel number+0/1”. “0” is used wheninforming transmission prohibition with respect to an initiallyoverlappingly allocated channel, and “1” indicates transmission allow.In a case of transmission allow in an initially allocated overlappingchannel, channel information may be omitted. In a case in which a rootAP temporarily allocates an additional channel, the number of theallocated additional channel may be indicated in a resource allocationIE.

(b) Option 2: indicates a bandwidth of a changed channel. In a case oftransmission disallow in an overlapping channel of a relay, a bandwidthmay be reduced compared to an initially allocated bandwidth and thus, aroot AP may transfer the reduced bandwidth to the relay. In a case inwhich the root AP temporarily allocates an additional channel, the rootAP may transfer information on an extended bandwidth using a resourceallocation IE. In this example, only changed bandwidth information isindicated and thus, a length of the resource allocation IE may notincrease although a plurality of channels is additionally allocated. Ina case of informing channel information, for example, a primary channel,a bandwidth, and a starting channel number allocated to a relay resourceallocation IE every time, there is no need to inform to which relay anoverlapping channel is allocated and which bandwidth is temporarilychanged.

In a case of informing, using a resource allocation IE, informationchanged from initial channel allocation in response to allocation of anoverlapping channel or allocation of a temporary additional channel, 1)a relay may inform a BSS bandwidth through a relay beacon in a case inwhich a bandwidth is temporarily changed over the entire relay beaconinterval. The relay may inform a relay BSS bandwidth using a fullbeacon. Also, in a case in which a relay beacon is provided in a shortbeacon format, the relay may inform STAs of a cluster of a change in therelay BSS bandwidth using a BSS bandwidth field of an FC of the relaybeacon. Also, 2) in a case in which a bandwidth of a relay BSS ischanged only in a portion of a relay beacon interval, the relay mayindicate channel information in a RAW for a duration in which thebandwidth is changed. For example, the relay may indicate the durationin which the bandwidth is changed, using “central frequency+channelbandwidth” or “bandwidth”. In a case in which a secondary channelincreases or decreases only in one direction, the relay may inform onlya changed bandwidth. A change in channel allocation may be allowed onlywith respect to a secondary channel of a relay BSS.

In a case of temporarily changing a channel allocated to a root AP, theroot AP may also inform channel allocation information by indicatingchannel information in a RAW for a changed time duration.

<(B) Resource Allocation Signaling Method in a Method of AllocatingResources Using Resource Allocation Information>

To inform resource allocation, an AID(s) of a relay allowed to performtransmission, a transmission allow starting time, a transmissionduration, resource allocation period information in a case in which aresource is periodically allocated, allocated frequency subbandinformation in a case in which multiple frequency subbands areallocated, information on additional resource allocation such asallocation of an overlapping channel/temporary channel, informationregarding whether another relay/STA is prohibited from performingtransmission in an allocated relay transmission duration, andinformation of a relay/STA prohibited from performing transmission maybe required. Subband allocation information, for example, defaultsubband allocation information may be shared between a relay and a rootAP when the relay is associated with the root AP. Thus, in addition to atemporary change such as allocation of an overlapping channel/temporarychannel, separate signaling may be omitted in a resource allocation IE.Channel information on a channel allocated to each relay may beexplicitly included in a resource allocation IE, and each of relays mayidentify channel allocation information of different relays through aroot beacon. Each of the relays may recognize a relay allocated to thesame channel of a corresponding relay through a root beacon. In a caseof explicitly informing channel information, for example, a primarychannel, a bandwidth, and a starting channel number allocated to aresource allocation IE every time, there is no need to inform to whichrelay an overlapping channel is allocated and which bandwidth istemporarily changed.

Also, a root AP and a relay may share information on a relay beaconinterval in advance through advance negotiation. The root AP mayallocate a relay transmission duration to transmit a relay beacon basedon the relay beacon interval. A relay resource allocation IE may beincluded in a root AP beacon and thereby transmitted. The relay resourceallocation IE may also be transmitted using a newly defined frame.

Hereinafter, a method of indicating resource allocation information in aresource allocation IE will be described.

1) Method of Indicating Resource Allocation Information for Each RelayAID

A relay AID(s), a relay start time, a duration, a period, and otherallocation information allocated in a short beacon interval of a root APmay be included in a resource allocation IE. For example, the otherallocation information may include allocated channel information orinformation on a strictly disallowed relay/STA.

In a case in which a resource is periodically allocated, there is noneed to transmit a relay resource allocation IE for each short beacon.For example, the relay resource allocation IE may be included only in acase of a long beacon transmission.

The following Table 3 shows an example of a resource allocation IEformat in a case of indicating resource allocation information for eachrelay AID. Referring to Table 3, a value of each field, a field order,and the like are only an example and thus, may be modified in a similarform.

TABLE 3 Feature Value Note Relay Partial AID(s) 9 bits describes relaythat is allowed to use corresponding resource. (In a case of allowingsimultaneous transmission of spatially separated relay BSSs, pluralityof AIDs may be designated.) 1 or more Start Time 8 bits In a case inwhich a plurality of time durations Duration TBD bits is inconsecutivelyallocated with respect to the same relay in single beacon interval,plurality of durations and start times may be included in a list.Additional Option 1- case of implicitly using channel allocationallocation information: is used when allowing information allocation ofan overlapping channel or (which is included allowing allocation oftemporary additional only in a case of channel, and includes temporarilychanged using bandwidth information. simultaneous Option 2 - case ofexplicitly using channel transmission of allocation information:explicitly indicates relay BSSs using channel information such as BW,primary frequency sub- channel, and starting channel number allocatedchannel) to relay BSS. In a case in which channel bandwidth is changedin consecutive duration, channel allocation information needs to beindicated by dividing start time/duration. To prevent the above event,root AP needs to allocate resources so that change in channel bandwidthmay be minimized in allocated consecutive duration. In a case in whichplurality of start times/durations is allocated and channel allocationinformation is identical to channel information allocated to previousstart time/duration, channel allocation information may be omitted.Period (Optional - present only in TBD bits is indicated using multipleof short beacon a case of performing periodic interval of a root AP.allocation) Strictly disallow 1 bit describes whether transmission ofpredetermined relay or STAs is to be explicitly prohibited in allocatedduration. List of Relay BSS (a STA 1 TBD bit describes strictlydisallowed relay or BSS in Relay BSS plurality of relay. and STAs relayBSSs describes single relay (Partial AID) + (multiple) can be disallowedSTA (partial) AID list in the designated) corresponding relay. Multiplerelay AID lists may be provided. STA N TBD bit When transmission of theentire relay BSS is disallowed, STA (partial) AID may be omitted, or maybe indicated using predetermined pattern, for example, 000..0 or 111.11.

Frequency sub-channel information of additional allocation informationmay be included in a case of performing simultaneous transmissionbetween relays using different frequency sub-channels. 1) In a case inwhich channel allocation information is implicitly indicated, that is,in a case in which a relay and a root AP share channel allocationinformation in advance between and separate relay information is notexplicitly indicated, a relay bandwidth may be indicated in a resourceallocation IE only in a case in which an initially allocated bandwidthis changed. For example, the relay bandwidth may be indicated in a caseof additional allocation of a temporary channel or transmission disallowin an overlappingly allocated channel. 2) In a case in which channelallocation information is explicitly indicated, channel information, forexample, a bandwidth, a primary channel, and a starting channel numberallocated to a relay BSS may be explicitly indicated in a resourceallocation IE.

In a case in which simultaneous transmission of spatially separatedrelay BSSs is allowed, a plurality of AIDs may be designated. Whenlocation information of two relays completely matches, a length of an IEmay be reduced using a plurality of AIDs. Although relay BSSs arespatially separated, each set of allocation information may be includedfor each AID when there is a difference in resource allocationinformation.

A strictly disallowed bit indicates whether transmission of apredetermined relay or STAs is explicitly prohibited in an allocatedduration. In a case in which the strictly disallowed bit is “1”,information on a strictly disallowed relay and STA may be included in anIE. The strictly disallowed bit may be used to indicate whethertransmission is disallowed with respect to the entire relay BSS orwhether transmission is disallowed with respect to a portion of STAs ina relay BSS.

In a single short beacon interval, a relay may list allocatedinconsecutive time durations as a list at a time and thus, may need toindicate resource allocation only once. When a relatively large numberof relays are used, a start time and an end time need to be indicatedfor each relay and thus, a length of a resource allocation IE mayincrease.

In a case in which there is a duration in which a bandwidth temporarilyvaries in a duration allocated to a relay, the duration may need to bedivided and thereby be indicated. However, if a root AP properly alignsa time, it may be possible to prevent the duration from being dividedand thereby being indicated. The same time duration may be allocated toa plurality of relays. In this example, the same time information mayneed to be indicated in relay allocation information to besimultaneously transmitted. In a case in which transmission is notcompleted in a time duration allocated to a predetermined relay cluster,a transmission duration allocated to be simultaneously used in aplurality of relay clusters may be used to complete the transmission.

FIG. 41 illustrates an example of a format of a relay resourceallocation IE of Table 3 according to an embodiment. Resource allocationinformation allocated to a plurality of relays may be included in therelay resource allocation IE for each AID. Resource allocationassociated with each relay may be defined in a relay N allocation field.A plurality of time durations allocated to a relay may be defined ineach relay N allocation field. For example, a time duration allocated toa relay may refer to a time duration allocated within a single rootbeacon.

2) Method of Indicating Allocation Information for Each FrequencySubband in which an Allocated Relay is Present

For example, allocation information may be indicated in a relay resourceallocation IE in a form of “{frequency subband, {relay AID allocated tofrequency subband, relay start time, duration+period, strictly disallow,list of strictly disallowed relay APs or STAs in the relay BSS} list}”for each frequency subband. Frequency subband allocation information foreach relay is shared when a corresponding relay is initially associatedwith a root AP and thus, may have no need to be indicated for eachfrequency subband.

3) Method of Indicating Resource Allocation Information for Each TimeDuration

FIG. 42 illustrates an example of allocating resources for each timeduration according to an embodiment. A beacon interval or a short beaconinterval may be divided into time durations. “{Start time,duration+period, {relay AID allocated to corresponding time duration,other allocation information, for example, channel allocationinformation, strictly disallow, list of strictly disallowed relay APs orSTAs in the relay BSS} list}” may be indicated in a relay resourceallocation IE for each time duration. Here, the time duration refers toa time duration longer than a RAW.

The following Table 4 shows a format of a resource allocation IE in acase of indicating allocation information for each time duration.

TABLE 4 Feature Value Interpretation Start Time 8 bits Duration TBD bitsRAW is allocated to each relay within this range. Period (Optional -case of periodic TBD bits Multiple of short beacon interval of rootallocation) AP Repeat number of Allocated relay 9 bits describes anallocated relay. times AID corresponding to Other allocation describesrelated information or explicit number of relays information relaychannel allocation information allocated to when allowing partialchannel corresponding time overlapping or allowing temporal durationallocation of additional channel. Strictly disallow describes whethertransmission of predetermined relay or STAs is to be explicitlyprohibited in allocated duration. List of relay BSS TBD bit describesstrictly disallowed relay or and STAs BSS in relay. Single relay(Partial AID) + disallowed STA (partial) AID list in the correspondingrelay may be listed. Multiple relay AID lists may be provided. TBD bitWhen transmission of the entire relay BSSs is disallowed, STA (Partial)AID may be omitted, or may be indicated using predetermined pattern, forexample, 000..0 and 111.11.

There is no need to indicate a start time and an end time of a timeduration a plurality of times for each relay. It is enough to indicatethe start time and the end time once for relays belonging to the sameduration. A format of a resource allocation IE may be similar to aformat of an RPS IE when using a RAW. When the number of relays allowedto perform transmission is relatively large in the same time durationand time durations are similar, a method of indicating resourceallocation information for each time duration may be appropriate. Whenthe number of relays is relatively small and time durations in whichrelays allowed to perform transmission significantly differ, a method ofindicating resource allocation information for each relay AID may beappropriate.

<(B) Transmission Duration Protecting Method in a Method of AllocatingResources Using Resource Allocation Information>

The method (B) of allocating resources using resource allocationinformation may also use an empty RAW for transmission durationprotection, which is similar to the method (A) using a DRAW.

In the method (A) using a DRAW, at a level 0, a root AP may use a DRAWto protect transmission of a relay cluster using the same frequencysubband as the root AP. Explicit transmission prohibition information ona transmission protection duration and relay resource allocationinformation on a DRAW duration may be included in the DRAW.

In the method (B) of allocating resources using resource allocationinformation, relay resource allocation information may be transferred ina form of a relay resource allocation IE, instead of being transferredin a form of a RAW. Similar to resource protection at a level 1 of themethod (A) using a DRAW, an empty RAW may be used for resourceprotection at a level 0. As another example, a method of allowingtransmission only in an explicitly allocated duration without using anempty RAW may be used for resource protection. A resource protectionmethod at a level 1 of the method (B) of allocating resources usingresource allocation information may use the method using an empty RAW orthe method of allowing transmission only in an explicitly allocatedduration.

The following Table 5 shows a format for empty RAW signaling used whenindicating a duration in which transmission of an STA (level 0 or 1)associated with an AP or a relay (level 0) is prohibited. Informationshown in Table 5 may be included in an RPS IE as RAW information.

TABLE 5 Feature Value Interpretation Empty RAW 1 bit describes whetherRAW corresponds indication to Empty RAW. Empty RAW 8 bits describespoint in time at which Empty Start Time RAW starts. Field present inconventional RPS IE may be used. In this example, Empty RAW Start Timeis defined as Duration in TU from end of beacon transmission to EmptyRAW Start time. Empty RAW TBD describes length of Empty RAW. Fieldpresent Duration bits in conventional RPS IE may be used. In thisexample, Empty RAW Duration is defined as Duration of Empty RAW in TU.

At a level 0, an empty RAW may be used to indicate a duration in whichtransmission of an STA associated with a root AP or transmission ofanother relay is prohibited in a transmission duration of a relay usingthe same frequency subband as the root AP. At a level 1, the empty RAWmay be used to indicate a duration in which transmission of an STA in arelay cluster is prohibited outside an explicitly allocated duration. Ina case in which the empty RAW is designated, transmission may beprohibited during a duration starting from an empty RAW start time andspecified as an empty RAW duration.

In the 802.11ah standard capable of explicitly indicating a duration inwhich an AP enters a power save mode, when an AP power save bit is setto “1” in an RPS IE, it indicates that the AP may be in a sleep state ina corresponding RAW duration and an STA may not perform transmissionwith respect to the corresponding AP. Empty RAW signaling may beperformed using the AP power save bit. For example, when an empty RAWsetting duration is set as a RAW and the AP power save bit is set to“1”, STAs may not perform transmission in a DRAW or RAW duration. Thus,the same effect as an effect of using an empty RAW may be achieved.

Conversely, an AP power save mode may be explicitly indicated byextending the empty RAW signaling method. When a duration in which an APperforms power saving is set as an empty RAW, an STA may not performtransmission in the duration set as the empty RAW and thus, the AP powersave mode may be explicitly indicated. In this example, since adefinition of the empty RAW may include a much fewer number of bits thana definition of a conventional RPS IE, it is possible to further reduceda length of the RPS IE by applying the empty RAW for to an AP power saveindication.

Alternatively, all of an empty RAW indication bit and an AP power savebit may be indicated in an empty RAW. Although transmission between arelay and an STA associated with the relay is disallowed in the emptyRAW for a level-1 duration, the relay may perform transmission with aroot AP in the level-1 duration and may not perform power saving inreality. Thus, in a case of using all of the empty RAW indication bitand the AP power save bit, whether the relay is in a sleep state inreality may be explicitly indicated. When using a power save bit in alevel-0 duration, a duration in which a root AP is not substantially ina sleep state in an empty RAW duration may be indicated. Also, the rootAP may allow an STA that is to be newly associated with the root AP toperform transmission in the empty RAW duration.

In a case in which an empty RAW is explicitly allocated periodically, aform of a PRAW may be used. In this example, 1 bit indicating whether aRAW corresponds to a PRAW, and information on an interval of the PRAWmay be additionally provided. For example, the interval of the PRAW maycorrespond to an integer value that indicates a multiple of a shortbeacon. Alternatively, 1 bit indicating whether a RAW corresponds to aPRAW may be omitted, and information on the interval of the PRAW may beadditionally included in a root beacon in addition to items listed inTable 1.

In a case in which transmission of an STA in a cluster is explicitlyprohibited outside a RAW, an empty RAW may not be used. At the level 0,a root AP may by allocate 1 bit in a root beacon and thereby mayindicate whether transmission is prohibited in a RAW not explicitlyallocated by the root AP. At the level 1, a relay may allocate 1 bit ina relay beacon and thereby may indicate whether transmission isprohibited in a RAW not explicitly allocated by a relay AP. For example,when the allocated bit corresponds to “1”, an STA may not performtransmission in durations other than a duration explicitly set as theRAW.

In the 802.11ah standard, a duration in which AP enters a power savemode may be implicitly indicated. For example, when an AP power save bitis set to “1” in a short beacon or a beacon, an STA may be prohibitedfrom performing transmission to an AP in durations other than anexplicitly allocated RAW duration.

At the level 1, whether transmission of an STA is prohibited indurations other than a RAW duration allocated by a relay may beindicated using an AP power save bit. In a case in which transmission ofan STA is to be prohibited in durations other than the RAW duration,when a relay sets the AP power save bit to “1” in a relay beacon, STAsmay be prohibited from performing transmission in a DRAW or RAWduration. At the level 0, when a root AP sets the AP power save bit to“1” in a root beacon, a relay or an STA directly associated with theroot AP may be prohibited from performing transmission in durationsother than a RAW explicitly allocated by the root AP.

The following Table 6 shows modified empty RAW signaling informationindicating that a predetermined STA is explicitly prohibited fromperforming transmission in a RAW duration.

TABLE 6 Feature Value Interpretation Empty RAW 1 bit describes whetherRAW corresponds indication to Empty RAW. Empty RAW 8 bits describespoint in time at which Empty Start Time RAW starts. Field present inconventional RPS IE may be used. In this example, Empty RAW Start Timeis defined as Duration in TU from end of beacon transmission to EmptyRAW Start time. Empty RAW TBD bits describes length of Empty RAW. Fieldpresent Duration in conventional RPS IE may be used. In this example,Empty RAW Duration is defined as Duration of Empty RAW in TU. List ofTBD bits describes (partial) AID list of STAs Prohibited prohibited fromperforming transmission STAs in empty RAW duration.

In an empty RAW duration, STAs specified in a list of prohibited STAsmay be prohibited from performing transmission, and other STAs notspecified therein may perform communication through empty RAW durationcontention. Also, by adding the list of prohibited STAs to an AP PM RAWof the 802.11ah standard, only STAs specified in the list of prohibitedSTAs may be prohibited from performing transmission. The above examplemay be applicable to both the method (A) using a DRAW and the method (B)of allocating resources using resource allocation information.

FIG. 43 illustrates an example of performing transmission using a relayresource allocation IE in a single frequency subband according to anembodiment.

Referring to FIG. 43, resource allocation information may be included ina separate relay resource allocation IE and thereby transferred. Aduration in which a resource is allocated may be explicitly protectedusing an empty RAW, or may be protected using an implicit method.

In a case in which transmission between STA-Relay-Root AP is performedin a single transmission opportunity (TXOP) using TXOP sharing, or in acase in which a predetermined STA transmits UL data to a relay in a ULslot of the STA in a transmission duration allocated to the relay and aslot still remains, the relay may directly transmit UL data to a rootAP. In this example, the root AP may set a duration allocated to therelay as an empty RAW, thereby preventing transmission of an STAbelonging to another root AP.

In a case of a DL, in a case in which a root AP transmits a DL frameabout a predetermined STA to a relay in a duration allocated as a DLduration, a DL transmission slot allocated by the root AP to the relayremains, and the STA to receive the DL frame is waked up, the relay mayimmediately transmit the DL frame to the STA.

As another example, a root AP may transmit a DL frame to a relay using aslot allocated so that an STA may receive the DL frame from the relay.In this example, the root AP may set a duration allocated to the relayas an empty RAW, thereby preventing transmission of an STA belonging toanother root AP. The relay may receive the DL frame about the STA fromthe root AP and then transmit the DL frame through a DL slot, forexample, the slot allocated by the relay, for the corresponding STA.

FIG. 44 illustrates another example of performing transmission using arelay resource allocation IE in a single frequency subband according toan embodiment.

The embodiment of FIG. 44 refers to another example of performingtransmission using the relay resource allocation IE in a singlefrequency subband. In this example, a method similar to a method using aDRAW is applied to resource allocation.

FIG. 45 illustrates an example of performing transmission using a relayresource allocation IE in multiple frequency subbands.

Referring to FIG. 45, a root AP may independently perform transmissionin a frequency subband different from a relay, and relays using subbandsA and B, respectively, may independently perform transmission. Sincefrequency subbands are mutually independent, time durations allocated tothe respective relays at a level 1 may have no need to be aligned basedon mutual time durations and may have no need to be aligned with a RAWof the root AP. Accordingly, enhanced flexibility and ease extensibilitymay be achieved compared to a case of using a DRAW.

The method (B) of allocating resources using resource allocationinformation may be applicable to all of the embodiments of FIGS. 23, 24,25, 26, 27, 28, and 31 described as an example of the DRAW, FIG. 37described as an example of simultaneous transmission in a case in whichrelay clusters are spatially separated, and FIG. 38 described as anexample of simultaneous transmission in a time domain.

<(AA) Method in which a Root AP Allocates a Relay Transmission DurationLength at a Level 1>

When a relay is associated with a root AP and then negotiates a relayrelated parameter with the root AP, the relay may request the root APfor a beacon interval to be used by the relay and a duration used for arelay to perform BSS transmission and may be allocated with an initialrelay BSS transmission duration from the root AP. Once transmissionbetween the relay and an STA starts, the relay may determine whetherallocation of a transmission duration for a relay BSS is furtherrequired or less required, and may feedback the determination result tothe root AP. The root AP may adjust the transmission duration for therelay BSS based on information fed back from the relay and mayreallocate the transmission duration to the relay BSS. The above methodmay be useful in a case in which an amount of traffic and a transmissioninterval are relatively constant. When transmission traffic and atransmission interval of an STA are not constant, the following method Dand method E may be employed to more accurately allocate thetransmission period of the relay BSS.

<Method D>

FIG. 46 illustrates an example of allocating a relay transmissionduration according to an embodiment. A relay may feedback a mean datarate of an STA to a root AP prior to transmitting a next deliverytraffic indication message (DTIM) of the relay. In a case of a targetwake time (TWT) STA, TWT information may also be transmitted in additionto the mean data rate.

In a case of an implicit TWT, a wake interval may be additionally fedback to the root AP. In this example, a TWT is periodically transferred.Thus, although the relay does not feedback a TWT every time, the root APmay add a wake interval to a previous TWT and thereby determine a nextTWT within a range in which the wake interval does not vary.

For example, a root AP may approximately determine the entire DLduration of a next TIM or DTIM duration based on “sum of (DL data sizebuffered for each STA to be set to TIM=1 with respect to next TIM orDTIM duration of relay beacon/mean data rate of each STA)+sum of datasize buffered for each TWT STA waking up in next TIM or DTIM durationand having buffered data/mean data rate of each STA)”.

For example, a root AP may determine a DL duration during a next relaybeacon interval for a relay BSS according to the following Equation 1.

$\begin{matrix}{{{Expected}\mspace{14mu}{DL}\mspace{14mu}{Duration}\mspace{14mu}{during}\mspace{14mu}{the}\mspace{14mu}{next}\mspace{14mu}{Relay}\mspace{14mu}{beacon}\mspace{14mu}{interval}} = {{\Sigma_{i}\left\lbrack {\left( \frac{{DataSizeBufferdForTIMESTA}(i)}{{MeanDLDataRateOfTIMSTA}(i)} \right)*{{TIMbit}(i)}{ForNextRelayBeacon}} \right\rbrack} + {\Sigma_{j}\left\lbrack {\left( \frac{{DataSizeBufferdForTWTSTA}(j)}{{MeanDLDataRateOfTWTSTA}(j)} \right)*W\mspace{11mu}\bullet\;{{thinNextRelayBeacon}(j)}} \right\rbrack}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

In Equation 1, DataSizeBufferedForTIMSTA(i) denotes a data size (bits)of TIM STA(i) buffered by the root AP, and MeanDLDataRateOfTIMSTA(i)denotes a mean DL data rate (bits/s) of TIM STA(i). When a TIM bit forTIM STA(i) is set to “1” in a relay beacon, TIMbit(i)ForNextRelayBeaconfor a next relay beacon is set to “1” and in other cases, TIMbit(i) forthe next relay beacon is set to “0”.

DataSizeBufferedForTWTSTA(j) denotes a data size (bits) of TWT STA(j)buffered by the root AP, and MeanDLDataRateOfTWTSTA(j) denotes a mean DLdata rate (bits/s) of TWT STA(j). When a target wake-up time of TWTSTA(j) is present within a next relay beacon interval, a value ofWithinNextRelayBeacon(j) interval is set to “1” and in other cases, avalue of WithinNextRelayBeacon(j) interval is set to “0”.

Transmission durations of a TWT STA may not be adjacent to each other.In this example, times between the transmission durations of the TWT STAmay be additionally added to a DL duration. Although a relay performsTIM segmentation, the relay may initially transmit a next relay beaconand then transmit remaining data when a time for first TIM segmenttransmission is insufficient.

A relay may transmit an expected data size to a root AP based ontransmission statistics of UL data obtained so far. To determine anexpected data size, a TIM STA may require information on an expecteddata size that is calculated based on a mean data rate (for UL) for arelay of an STA, and UL data transmission statistics of the STA obtainedso far. To determine an expected data size, a TWT STA may also need toadditionally transmit TWT information to the root AP. An implicit TWTmay additionally transmit wake interval information to the root AP.

For example, a time duration required to transmit UL data in a relay BSSmay be determined according to the following Equation 2.

$\begin{matrix}{{{Expected}\mspace{14mu}{UL}\mspace{14mu}{Duration}\mspace{14mu}{during}\mspace{14mu}{the}\mspace{14mu}{next}\mspace{14mu}{Relay}\mspace{14mu}{beacon}\mspace{14mu}{interval}} = {\Sigma_{i}\left\lbrack {\left( \frac{{MeanULDataSizeForTIMESTA}(i)}{{MeanULDataRateOfTIMSTA}(i)} \right) + {\Sigma_{j}\left\lbrack {\left( \frac{{MeanULDataSizeForTWTSTA}(j)}{{MeanULDataRateOfTWTSTA}(j)} \right)*{{WithinNextRelayBeacon}(j)}} \right\rbrack}} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

In Equation 2, MeanULDataSizeForTIMSTA(i) denotes a mean UL data size(bits) for TIM STA(i), and MeanULDataRateOfTIMSTA(i) denotes a mean ULdata rate for TIM STA(i). MeanULDataSizeForTWTSTA(j) denotes a mean ULdata size (bits) for TWT STA(j), and MeanULDataRateOfTWTSTA(j) denotes amean UL data rate for TWT STA(j).

When a target wake up time of TWT STA(j) is present within a next relaybeacon interval, a value of WithinNextRelayBeacon interval is set to “1”and in other cases, a value of WithinNextRelayBeacon interval(j) is setto “0”.

Transmission durations of a TWT STA may not be adjacent to each other.In this example, times between the transmission durations of the TWT STAmay be additionally added to a DL duration.

Instead of feeding back, to a root AP, each of a mean UL data size forTWT STA, a mean UL data rate for TWT STA, a mean UL data size for TIMSTA, and a mean UL data rate for TIM STA, a relay may directly calculatea value of (mean UL data size for TWT STA)/(mean UL data rate for TWTSTA) and a value of (mean UL data size for TIM STA)/(mean UL data ratefor TIM STA) and thereby feedback the same to the root AP.

For example, an expected UL duration during a next relay beacon intervalmay be determined according to the following Equation 3.Expected UL Duration during the next Relay beaconinterval=Σ_(i)(MeanULDurationForTIMSTA(i))+Σ_(j)[(MeanULDurationForTWTSTA(j))*WithinNextRelayBeacon(j)]  [Equation3]

In Equation 3, when a target wake up time of TWT STA(j) is presentwithin a next relay beacon interval, a value of WithinNextRelayBeaconinterval is set to “1” and in other cases, a value ofWithinNextRelayBeacon interval(j) is set to “0”.

MeanULDurationForTIMSTA(i) denotes (mean UL data size (bits) for TIMSTA(i))/(mean UL data rate (bits/s) for TIM STA(i)).MeanULDurationForTWTSTA(j) denotes (mean UL data size (bits) for TWTSTA(j))/(mean UL data rate (bits/s) for TWT STA(j)).

The transmission duration of the entire relay BSS may be calculatedbased on the calculated UL duration and DL duration for the relay BSSaccording to the following Equation 4.Transmission Duration of entire Relay BSS=Expected DL Duration duringthe next Relay Beacon Interval+Expected UL Duration during the nextRelay Beacon Interval+Expected PS-Poll Duration during the next RelayBeacon Interval  [Equation 4]

An STA information announcement frame defined in the 802.11ah standardmay be extended and thereby used. For example, an additional element ofthe STA information announcement frame may be defined to include AIDupdate information and duration allocation related information in theSTA information announcement frame. Alternatively, a new frame capableof including duration allocation related information may be defined, anda relay may transmit the newly defined frame to a root AP. The relay mayhave no need to update all the STA information for each DTIM, and mayupdate information on only an STA of which a data rate is significant.

<Method E>

In an initial stage, a root AP may allocate a transmission time of arelay beacon and an initial transmission duration based on a totalnumber of relays included in an extended BSS. A relay may transfer, tothe root AP, a relay setup request about an initial transmissionduration and a relay beacon interval. In response to the relay setuprequest, the root AP may transfer, to the relay, a relay setup responseabout a next relay target beacon transmission time (TBTT) and a beaconinterval and an initial duration.

Update of a transmission duration may be performed using Option 1 andOption 2 as follows.

(1) Option 1: In a case in which traffic of an STA associated with arelay is regular, a root AP may periodically allocate a transmissionduration, and may adjust the transmission duration only in a case inwhich the relay explicitly requests update of the transmission duration.

(2) Option 2: In a case in which traffic of an STA associated with arelay is irregular, a root AP may adjust a transmission duration basedon information on each STA of the relay. The relay may transmit, to theroot AP, information received from an STA when the STA is associatedwith the relay and additional information using a ReachableAddressUpdateframe, and the root AP may adjust a transmission duration within a relaycluster based on information received from the relay. At a point in timewhen each STA is associated with the relay, the relay may transmit, tothe root AP, information on a reachable address, for example, a MACaddress of a corresponding STA, a mean data rate, an AID of the STA, andan STA Type. The mean data rate uses an initial value (4 octets)transmitted to the relay when the STA is initially associated with therelay. At a time just ahead of a DTIM transmission time of the relay,the relay may transmit, to the root AP, information on a number of TIMsegments of a next DTIM duration of the relay (+TIM Offset, PageOffset), an updated mean data rate, and an AID of a reallocated STA. Theupdated mean data rate and the AID of the reallocated STA may betransmitted when it is required for each STA.

A root AP may determine when a relay DTIM is to be transmitted based ona relay beacon. The root AP may determine in which beacon after a DTIM aTIM segment for a predetermined STA is transferred based on a number ofTIM segments and an AID of an STA. The relay schedules DL transmissionfor an STA in a TIM segment and thus, the root AP may predicttransmission from the relay to the STA in a relay beacon interval.

The root AP may predict a time required for DL transmission in apredetermined relay beacon interval based on an amount of traffic for anSTA, a mean data rate, and a relay beacon interval in which DL data istransmitted. In a case of a TWT STA, the root AP may predict a timerequired for DL transmission in a predetermined relay beacon intervalbased on a TWT, transmission duration information, and mean data rateinformation.

The root AP may determine a UL transmission duration based on STA typeinformation transferred when an STA is associated with a relay. Therelay may allocate an allocated transmission duration in detail as, forexample, a UL RAW and a DL RAW. In a case in which a transmissionduration is insufficient, the root AP, the relay, and the STA may bufferdata and transmit the buffered data in a next transmission duration.

<(BB) Method of Determining a Spatial Separation Between Relays>

In an initial stage, a relay may measure a degree of spatial separationbetween a root AP and another relay BSS, and may transfer themeasurement result to the root AP. The root AP may allocate atransmission duration of a relay BSS based on the measurement resultreceived from the relay. When a new relay BSS and the other relay BSSare spatially sufficiently separated from each other, the root AP mayoverlappingly allocate a transmission duration.

Also, to prevent collisions occurring when an STA belonging to a relayBSS transmit data in a transmission duration for another relay BSS usingthe same channel, the relay BSS may explicitly set the transmissionduration of the other relay BSS as an empty RAW or an AP PM RAW. Therelay BSS may periodically determine whether the relay BSS is spatiallyseparated from the other relay BSS. When the relay BSS is insufficientlyseparated from the other relay BSS, the relay BSS may prohibit datatransmission of an STA associated with the relay BSS by setting thetransmission duration of the other relay BSS as an empty RAW or an AP PMRAW. Alternatively, instead of prohibiting all the STAs in the relay BSSfrom performing data transmission in the transmission duration of theother relay BSS, the relay BSS may prohibit transmission of only apredetermined STA affected by relatively great interference of the otherrelay BSS among the STAs in the relay BSS. In this example, a methodusing a modified empty RAW or a modified AP PM RAW capable of explicitlyindicating an STA prohibited from performing transmission or a method ofexcluding an STA prohibited from performing transmission from atransmission duration allocation target may be used.

Similarly, to prevent collisions occurring when an STA belonging to aroot BSS transmit data in a transmission duration for another relay BSSusing the same channel, the root BSS may explicitly set the transmissionduration of the other relay BSS as an empty RAW or an AP PM RAW. Usingthe following method, the root BSS may determine whether the root BSS isspatially separated from the other relay BSS. When the root BSS isinsufficiently separated from the other relay BSS, the root BSS mayprohibit data transmission of an STA associated with the root BSS bysetting the transmission duration of the other relay BSS as an empty RAWor an AP PM RAW. Alternatively, instead of prohibiting all of the STAsin the root BSS from performing data transmission in the transmissionduration of the other relay BSS, the root BSS may prohibit transmissionof only a predetermined STA affected by relatively great interference ofthe other relay BSS among the STAs in the root BSS. In this example, amethod using a modified empty RAW or a modified AP PM RAW capable ofexplicitly indicating an STA prohibited from performing transmission ora method of excluding an STA prohibited from performing transmissionfrom a transmission duration allocation target may be used.

In level-1 transmission, although a transmission duration is notallocated to a relay to which an STA belongs, the STA may be allowed toperform transmission, as an exception, in a transmission duration notexplicitly set as an empty RAW, in a case in which transmission ofanother relay BSS is not detected or in a case in which a RAW is not setwithin a duration allocated for transmission of a corresponding relayBSS based on a determination result made based on a beacon of thecorresponding relay BSS.

In level-0 transmission, although a time duration is allocated toanother relay BSS, an STA of a root BSS may perform transmission, as anexception, in the corresponding time duration, in a case in whichtransmission of the other relay BSS is not detected or in a case inwhich a RAW is not set within a duration allocated for transmission of acorresponding relay BSS based on a determination result made based on abeacon of the corresponding relay BSS.

Alternatively, an STA belonging to a root AP and an STA belonging to arelay may be allowed to perform transmission through contention, similarto transmission in a conventional OBSS environment, even in a durationin which transmission of the STAs to an AP is not allowed. However,since a probability of collisions may be relatively high in a case inwhich data is transmitted in a duration not allocated to a BSS to whichan STA belongs, the STA may perform RTS/CTS in advance of datatransmission.

A relay or a root AP may explicitly prohibit transmission of STAsassociated with the relay or the root AP by setting, as an empty RAW, aduration in which intense collision or contention is expected amongtransmission durations not allocated to the relay or the root AP. Also,a relay AP may prohibit an STA from performing transmission to a relayin a duration in which transmission between the relay and the root AP isperformed, by setting, as an empty RAW, the duration in which thetransmission between the relay and the root AP is performed. Forexample, the relay or the root AP may prohibit all the STAs associatedwith the relay from performing transmission in a predetermined durationby setting AP PM=1. The AP PM denotes a parameter for adjusting a powersave mode of a station.

<A. Method of Determining Spatial Separation>

A first method of determining a degree of spatial separation refers to amethod of extending a frame request/response frame defined in 802.11kand thereby determining whether STAs belonging to a relay BSS areseparated from a relay of a neighboring relay BSS and an STA belongingto the neighboring relay BSS. FIG. 47 illustrates a format for a framerequest according to an embodiment, and FIG. 48 illustrates a format fora frame report according to an embodiment. An STA may detect a receivedchannel power indicator (RCPI) and a received signal to noise indicator(RSNI) for a transmission frame of an STA belonging to another relayBSS, and may report the detected RCPI and RSNI.

Using a beacon report, RCPI and RSNI values for an AP may be identified.Using a frame report, the average RCPI value and the average RSNI valuefor a predetermined STA may be identified through predetermined frametransmission that is performed by the STA.

A frame measurement request for an STA using a predetermined MAC addressas a target may be included in a beacon request. Here, a wildcard MACaddress may be designated.

A frame report may include a frame count report subelement in an opticalsubelement. A count, that, the number of frames transmitted from asingle STA and information on the average RCPI value and the averageRSNI value may be included in a single report entry. Based on the framecount and the average RCPI value and the average RSNI value, a degree ofspatial separation with a predetermined STA may be determined.

—Extension of Frame Request/Response Frame into Consideration of Relay—

FIG. 49 illustrates an example of a format of a management request fieldaccording to an embodiment, and FIG. 50 illustrates an example of aformat of a management report field according to an embodiment.

To determine whether a predetermined relay and an STA are separated fromeach other, a frame request/response frame may be extended to measure aframe to be transmitted from or to a predetermined BSSID. The framerequest/response frame may be extended to be capable of adding a BSSIDto an optional subelement of an existing format.

When a MAC address is a wildcard and a BSSID is designated in asubelement, a frame request/response frame may be extended to measure aframe transmitted from the corresponding BSSID and a frame to betransmitted to the corresponding BSSID.

In the extended frame request/response frame, a measurement start timemay be designated in addition to a measurement duration. When requestinga frame report, the measurement start time may be set as a transmissionduration start time allocated to a relay BSS to be measured. In ordernot to interrupt transmission of another relay, STAs may perform onlymeasurement in a transmission duration of another relay BSS and maytransmit a measurement report later. A RAW for transmission of themeasurement report may be allocated.

STAs may receive a request for a measurement report usingbroadcast/groupcast during a transmission duration of a relay BSS. Amongthe STAs, STAs supporting a 802.11k function may perform measurementwith respect to a designated relay in a designated starttime/transmission duration and may transmit the measurement result to arelay with which the STAs are associated. The relay receiving themeasurement result may determine whether the relay is separated from aneighboring relay based on the measurement result.

To decrease an amount of traffic, a method of selecting an STA thatbelongs to a relay and supports predetermined 802.11k may be used. It isbecause when a measurement report is received from all of the STAsbelonging to a relay, an amount of traffic may overly increase. Forexample, the relay may select a predetermined STA from among STAssupporting 802.11k, and may request the selected STA for a measurementreport.

A relay may also request an STA performing measurement to transmitinformation, for example, the average RCPI value and the average RSNIvalue or a maximum RCPI value and a maximum RSNI value, with respect tothe entire transmission of a predetermined BSS, instead of transmittinginformation for each STA address. To reduce a size of a measurementreport, the relay may request an STA to transmit not RCPI and RSNIvalues for each STA but the average RCPI value and the average RSNIvalue or RCPI and RSNI values, for example, a maximum RCPI value and amaximum RSNI value of an external STA that most greatly affects thecorresponding relay.

To indicate the entire BSS information, a BSS frame count reportmodified from an existing frame report entry may be defined. That is, byfurther shortening an existing frame count report, the BSS frame countreport including a BSSID, an average transmission frame count within theBSSID, the average RCPI value and the average RSNI value may be defined.

Each relay may request STAs belonging thereto for a frame report, andmay determine whether the STAs and a neighboring relay BSS are separatedfrom each other, based on the frame report. A root AP may also requestSTAs belonging to the root AP for a frame report, and may determinewhether STAs belonging to each root BSS and a neighboring relay BSS areseparated from each other.

A relay AP or a root AP may determine whether a BSS of the relay AP orthe root AP and a predetermined relay BSS are separated from each other,and may determine whether a transmission duration of another relay BSSis to be set as an empty RAW. In a case in which the BSS of the relay APor the root AP and the predetermined relay BSS are determined to beinsufficiently separated from each other, the relay AP or the root APmay set the transmission duration of the other relay BSS as an empty RAWor AP PM=1, thereby prohibiting an STA belonging to the BSS of the relayAP or the root AP from transmitting data in the other relay transmissionduration.

According to another embodiment, a relay AP or a root AP may identifySTAs insufficiently separated from another relay based on a measurementreport received from an STA belonging to the relay AP or the root AP.The relay AP or the root AP may prohibit STAs insufficiently separatedfrom the other relay from performing transmission in a transmissionduration of the other relay. That is, instead of prohibiting the entireSTAs included in a BSS of the relay AP or the root AP from performingtransmission, the relay AP or the root AP may prohibit only a portion ofSTAs affected by interference of a predetermined relay BSS fromperforming transmission. In this example, to prohibit a predeterminedSTA in a root BSS or a relay BSS from performing transmission, twomethods may be employed. For example, (1) a method of modifying andthereby using an AP PM or an empty RAW and (2) a method using existingRAW allocation may be employed. The method (1) of modifying and therebyusing an AP PM or an empty RAW is a method of including an AID orpartial AID list of an STA to be prohibited from performing transmissionin a transmission duration in an AP PM RAW or an empty RAW, andexplicitly disallowing only the STA included in the AID or partial AIDlist to perform transmission and allowing remaining STAs to performtransmission through contention in an AP PM RAW or empty RAW duration.The method (2) using an existing RAW allocation is a method ofdisallowing a corresponding STA to perform transmission by notallocating a RAW to an STA to be explicitly prohibited from performingtransmission when allocating a RAW for another relay transmissionduration.

When a relay requests a root AP for a BSS establishment in an initialstage, the relay may transmit, to the root AP, information regardingwhether the relay is separated from a neighboring relay. The root AP mayallocate the same transmission duration to spatially separated relayBSSs based on information received from the relay.

Also, a relay may periodically or aperiodically measure a degree ofspatial separation with another relay BSS. When the degree of spatialseparation with the other relay BSS is modified by a predeterminedreference or more, the relay may feedback the modified contents to aroot AP. For example, when a relay is affected by great interference ofexisting separated another relay BSS, the relay may inform the root APof the above situation. Alternatively, when a new relay BSS is detected,the relay may inform the root AP of the detected new relay BSS. The rootAP may also allocate the same duration for transmission of the spatiallyseparated relays, based on spatial separation information between therelays.

To reduce a length of a measurement report, a reporting option similarto a beacon report may be added to a frame request. For example, thereporting option may be set to include values greater than or equal toor less than or equal to predetermined RCPI and RSNI values in ameasurement report.

<B. Method of Determining Spatial Separation>

A second method of determining a degree of spatial separation refers toa method of using a beacon request/response defined in 802.11k. FIG. 47illustrates a format for a frame request according to an embodiment, andFIG. 48 illustrates a format for a frame report according to anembodiment.

A root AP may transmit a beacon request frame to a relay and an STAassociated with the root AP. Through a beacon request/report, an STA mayrequest another STA for a list of APs transmitting a receivable beacon.Since relays may use the same SSID as the root AP, the root AP mayinclude an SSID of the root AP in an optional subelement to receive abeacon report from a new STA. A BSSID may be set as a wildcard BSSID.

A newly established relay may receive a beacon request from a root APand then may measure a probe response and a beacon of another relay andtransfer the measurement result to the root AP through a beacon report.The root AP may allocate a transmission duration for the newlyestablished relay based on an RCPI and an RSNI between the newlyestablished relay and another relay AP.

A root AP may also transfer a beacon request after a relay is newlyestablished, and may update resource allocation based on a degree ofspatial separation.

When STAs are associated with a relay BSS, each relay may randomlyselect a portion of the STAs having a measurement function, and maytransfer a beacon request to the selected STAs. In this instance, aBSSID of the beacon request may be set as a wildcard BSSID, and an SSIDof an optional subelement may be set as an SSID of a root AP.

A relay may set a reporting condition of a beacon request. Thus, in acase in which the reporting condition of the beacon request is greaterthan or equal to, or less than or equal to a predetermined RCPI leveland a predetermined RSNI level, the beacon report may be transmitted.

A relay may periodically or aperiodically determine whether an STA isspatially separated from another relay based on a beacon report receivedfrom each of STAs. When the STA is determined to be spatially adjacentto the other relay, the relay may set a transmission time of the otherrelay as an empty RAW, thereby prohibiting transmission of thecorresponding STA.

Each relay may determine whether each of stations belonging to acorresponding relay is spatially separated from a neighboring relay,based on a beacon report received from each STA. A root AP may alsodetermine whether each of STAs directly associated with the root AP isspatially separated from a neighboring relay, based on a beacon reportreceived from each STA.

A relay AP or a root AP may determine whether a BSS of the relay AP orthe root AP is spatially separated from another relay, and may determinewhether another relay transmission duration is to be set as an empty RAWor an AP PM RAW. In a case in which a BSS of the relay AP or the root APis spatially insufficiently separated from the other relay, the relay APor the root AP may set an empty RAW or AP PM=1, thereby prohibiting anSTA belonging to the BSS of the relay AP or the root AP from performingtransmission in another relay transmission duration.

According to another embodiment, a relay AP or a root AP may identifySTAs insufficiently separated from another relay based on a measurementreport received from an STA belonging to the relay AP or the root AP.The relay AP or the root AP may prohibit STAs insufficiently separatedfrom the other relay from performing transmission in a transmissionduration of the other relay. That is, instead of prohibiting the entireSTAs included in a BSS of the relay AP or the root AP from performingtransmission, the relay AP or the root AP may prohibit only a portion ofSTAs affected by interference of a predetermined relay BSS fromperforming transmission. In this example, to prohibit a predeterminedSTA in a root BSS or a relay BSS from performing transmission, twomethods may be employed. For example, (1) a method of modifying andthereby using an AP PM or an empty RAW and (2) a method using existingRAW allocation may be employed. The method (1) of modifying and therebyusing an AP PM or an empty RAW is a method of including an AID orpartial AID list of an STA to be prohibited from performing transmissionin a transmission duration in an AP PM RAW or an empty RAW, andexplicitly disallowing only the STA included in the AID or partial AIDlist to perform transmission and allowing remaining STAs to performtransmission through contention in an AP PM RAW or empty RAW duration.The method (2) using an existing RAW allocation is a method ofdisallowing a corresponding STA to perform transmission by notallocating a RAW to an STA to be explicitly prohibited from performingtransmission when allocating a RAW for another relay transmissionduration.

When a relay requests a root AP for a BSS establishment in an initialstage, the relay may transmit, to the root AP, information regardingwhether the relay is separated from a neighboring relay. The root AP mayallocate the same transmission duration to spatially separated relayBSSs based on information received from the relay.

Also, a relay may periodically or aperiodically measure a degree ofspatial separation with another relay BSS. When the degree of spatialseparation with the other relay BSS is modified by a predeterminedreference or more, the relay may feedback the modified contents to aroot AP. For example, when a relay is affected by great interference ofexisting separated another relay BSS, the relay may inform the root APof the above situation. Alternatively, when a new relay BSS is detected,the relay may inform the root AP of the detected new relay BSS. The rootAP may also allocate the same duration for transmission of spatiallyseparated relays, based on spatial separation information between suchrelays.

The above method of measuring an interference level between relay BSSsmay be applicable to a method of measuring an interference level betweenmultiple BSSs in a WLAN as well as an interference level between relays.

FIG. 51 illustrates a method of measuring an interference level from aneighboring relay or a neighboring relay BSS using a framerequest/response according to an embodiment.

Referring to FIG. 51, a relay AP or a general AP, R1, may select STAs toperform measurement from among STAs associated with the relay AP R1, andmay transmit a frame request to the selected STAs. Each of STAs withinan R1 BSS having received the frame request may measure separationinformation on a neighboring relay BSS or a general BSS that uses R2 asan AP, and may transmit a measurement result to R1 in a form of a framereport. STAs within the R1 BSS having received the frame request maymeasure a frame that is transmitted from each of STAs within theneighboring BSS, for example, R2 during a measurement time. For example,separation information may include a separation level between an STA andR2 that is an AP, or between the STA and STAs associated with R2. R1 maymeasure an interference level from a neighboring BSS based on RCPI andRSNI information included in a frame report transferred from each STA.

FIG. 52 illustrates a configuration of an AP 5200 according to anembodiment.

Referring to FIG. 52, the AP 5200 may include a resource allocator 5210and a communication unit 5220.

The resource allocator 5210 may allocate a resource for communicationbetween a relay and an STA associated with the relay. The resourceallocator 5210 may allocate a transmission period or a frequency subbandfor communication between the relay and the STA associated with therelay.

The resource allocator 5210 may delegate, to the relay, detailedresource allocation with respect to STAs associated with the relay. Forexample, the resource allocator 5210 may allocate, to the relay, atransmission duration for communication between the relay and the STAassociated with the relay. The relay may divide the allocatedtransmission duration into sub-transmission durations for the respectiveSTAs. The relay may allocate a resource to STAs included in a relay BSS.

Also, the resource allocator 5210 may allocate a resource forcommunication with an STA directly associated with the AP 5200 withoutusing the relay. The resource allocator 5210 may control the STAdirectly associated with the AP 5200 not to perform communication duringthe transmission period allocated for the communication between therelay and the STA associated with the relay.

According to another embodiment, the resource allocator 5210 maydirectly allocate a resource to the entire STAs included in a root APBSS. That is, the resource allocator 5210 may also allocate a resourceto the STA associated with the relay as well as the STA directlyassociated with the AP 5200. For example, the resource allocator 5210may allocate a RAW or a slot for each of the STAs included in the rootAP BSS. The resource allocator 5210 may also allocate a RAW or a slotfor communication between the relay and the STA associated with therelay as well as communication between the AP 5200 and the STAassociated with the AP 5200. The RAW or the slot may refer to atransmission duration in a time domain, and a time domain in whichcommunication is allowed may be determined based on the RAW or the slot.The RAW or the slot may include a DL transmission duration or an ULtransmission duration.

The resource allocator 5210 may allocate a resource for communicationbetween the relay and the STA associated with the relay based on adegree of spatial separation between relays. The resource allocator 5210may determine a degree of spatial separation between the relay andanother relay, and may allocate a resource based on the determinationresult. For example, in a case in which the relay is determined to bespatially separated from the other relay by a predetermined distance ormore, the resource allocator 5210 may allocate the same or overlappingtransmission duration to the relays.

The resource allocator 5210 may allocate a resource based on a frequencysubband for communication between the relay and the STA associated withthe relay and a frequency subband for communication between the AP 5200and the relay. For example, when a frequency subband used forcommunication between the relay and the STA associated with the relayand a frequency subband used for communication between the AP 5200 andthe relay do not overlap, the resource allocator 5210 may allocate thesame or overlapping transmission duration for both communications.

The communication unit 5220 may transmit, to the relay, resourceallocation information on the resource allocated by the resourceallocator 5210. The communication unit 5220 may transmit, to the relay,resource allocation information on a resource allocated forcommunication between the relay and the STA associated with the relay.For example, resource allocation information may include at least one oftransmission duration information for communication between the relayand the STA associated with the relay, information on the allocatedfrequency subband, information on an allocated channel, and informationon a relay or an STA prohibited from performing communication in apredetermined duration. Resource allocation information may betransmitted in a form of a resource allocation IE. Resource allocationinformation may be indicated based on at least one of ID information ofthe relay, the frequency subband, and the time duration. Thecommunication unit 5220 may periodically or aperiodically transmit abeacon including resource allocation information.

The resource allocator 5210 may adjust the allocated resource based oninterference information or STA information received from the relay. STAinformation may include information on at least one of a data rate usedfor communication between the STA and the relay and a size of datatransmitted between the STA and the relay. The communication unit 5220may transmit information on the adjusted resource to the relay.

The relay may transmit, to the AP 5200, PS-Poll information and UDIinformation received from the STA. The resource allocator 5210 mayadjust the allocated RAW or slot based on the PS-Poll information andUDI information received from the relay. UDI information may includeinformation on an amount of data transmitted from the STA to the relay.PS-Poll information may indicate information transmitted to the relay orthe AP 5200 in order to receive a frame buffered during a power savemode after the STA is released from the power save mode.

FIG. 53 illustrates a configuration of a relay 5300 according to anembodiment.

Referring to FIG. 53, the relay 5300 may include a resource allocator5310 and a communication unit 5320.

The resource allocator 5310 may allocate a resource for communicationbetween the relay 5300 and an STA associated with the relay 5300 basedon resource allocation information received from an AP. For example, theresource allocator 5310 may allocate an access window or a slot forcommunication with the STA based on at least one of channel stateinformation, MCS information supported by the STA, available frequencysubband information, and the number of antennas of the STA.

The resource allocator 5310 may allocate a RAW or a slot forcommunication between the relay 5300 and the STA associated with therelay 5300 based on resource allocation information. For example, theresource allocation information may include a transmission duration forcommunication between the relay 5300 and the STA associated with therelay 5300. The resource allocator 5310 may divide he transmissionduration identified from the resource allocation information intosub-RAWs for the respective STAs.

In a case in which interference occurs between the STA associated withthe relay 5300 and another relay BSS, the resource allocator 5310 mayprohibit the entire or a portion of STAs associated with the relay 5300from performing transmission in a transmission duration allocated to theother relay BSS. For example, the resource allocator 5310 may set apartial communication duration as an empty RAW or an AP PM RAW so thatthe STA associated with the relay 5300 may not perform communication ina communication duration between the AP and an STA directly associatedwith the AP and in a communication duration of another relay.

The relay 5300 may transmit, to an STA, a measurement request formeasuring a frame transmitted from a predetermined BSSID or a frametransmitted to the predetermined BSSID. In response to the measurementrequest, the STA may transmit a measurement report to the relay 5300.The measurement report may include information on the frame transmittedfrom the predetermined BSSID or the frame transmitted to thepredetermined BSSID. For example, the measurement report may includeinformation on at least one of the number of frames transmitted fromanother relay, the number of frames transmitted to the other relay, andan RCPI and an RSNI related to a transmission frame of an STA associatedwith the other relay. The resource allocator 5310 may determine aspatial separation with the other relay based on the measurement reportreceived from the STA, and may allocate a resource for the STA based onthe determination result.

The communication unit 5320 may receive resource allocation informationfrom the AP. The communication unit 5320 may transmit, to the STA,information on the resource allocated by the resource allocator 5310.The communication unit 5320 may periodically or aperiodically transmit,to the STA, a beacon including information on the allocated resource.For example, the communication unit 5320 may transmit the beacon at astart time of a relay transmission duration indicated in resourceallocation information.

The beacon may include information on a RAW or a slot for communicationbetween the relay 5300 and the STA associated with the relay 5300.Information on a RAW or slot for communication between the AP and therelay 5300 may not be included in a beacon to be transmitted by thecommunication unit 5320. The communication unit 5320 may transmit, tothe AP, STA information on the STA associated with the relay 5300.

FIG. 54 illustrates an STA 5400 according to an embodiment.

Referring to FIG. 54, the STA 5400 may include a controller 5410 and acommunication unit 5420.

The communication unit 5420 may receive a beacon from a relay, and thecontroller 5410 may identify a resource allocated to the STA 5400 basedon the beacon received from the relay. The beacon received from therelay may include information on a resource allocated by the relay.

The controller 5410 may identify, from the received beacon, informationon at least one of a RAW or a slot indicating a communication durationin a time domain and a frequency subband indicating a communicationduration in a frequency band.

The communication unit 5420 may communicate with the relay based on theidentified resource. The communication unit 5420 may communicate withthe relay based on the identified RAW or slot, or frequency subband. Forexample, the communication unit 5420 may receive data from the relay ina RAW duration in which DL transmission is allowed, and may transmitdata to the relay in a RAW duration in which UL transmission is allowed.

FIG. 55 is a flowchart illustrating a resource allocation methodperformed by an AP according to an embodiment.

In operation 5510, the AP may allocate a first resource forcommunication between the AP and a relay and communication between theAP and an STA associated with the AP. The AP may allocate a RAW or aslot for communication between the AP and the relay and communicationbetween the AP and the STA associated with the AP. The RAW or the slotmay be used to determine a time domain in which communication isallowed. The RAW or the slot may include a DL transmission duration andan UL transmission duration.

In operation 5520, the AP may allocate a second resource forcommunication between the relay and the STA associated with the relay.The AP may allocate at least one of a transmission period and afrequency subband for communication between the relay and the STAassociated with the relay. The AP may allocate a RAW or a slot forcommunication between the relay and the STA associated with the relay.

In operation 5530, the AP may transmit, to the relay, resourceallocation information on the allocated second resource. Resourceallocation information may include information on at least one of IDinformation of the relay, a transmission allow start time, atransmission duration, a resource allocation period, an allocatedchannel, an allocated frequency subband, and a relay or an STAprohibited from performing communication in a predetermined transmissionduration. For example, ID information of the relay may include at leastone of an AID, a partial AID, and a partial BSSID of the relay. The APmay transmit, to the relay, a beacon including information on theallocated first resource and second resource.

In operation 5540, the AP may adjust the allocated second resource basedon interference information or STA information received from the relay.STA information may include information on at least one of a data rateused for communication between the relay and an STA associated with therelay and a size of data transmitted between the relay and the STAassociated with the relay.

Alternatively, the AP may adjust the resource allocated forcommunication between the relay and the STA associated with the relaybased on PS-Poll information and UDI information received from therelay.

FIG. 56 is a flowchart illustrating a resource allocation methodperformed by a relay according to an embodiment.

In operation 5610, the relay may receive resource allocation informationfrom an AP. Resource allocation information may include information onat least one of a transmission duration for communication between therelay and an STA associated with the relay, an available frequencysubband, and an available channel.

In operation 5620, the relay may allocate a resource for communicationbetween the relay and the STA associated with the relay, based onresource allocation information. The relay may determine a RAW or a slotfor communication between the relay and the STA based on resourceallocation information. The RAW or the slot may be used to determine atime domain in which communication between the relay and the STA isallowed.

According to another embodiment, the relay may request the STA formeasuring the number of frames transmitted from another relay, thenumber of frames transmitted to the other relay, or an RCPI and an RSNIrelated to a transmission frame of an STA associated with the otherrelay. In response to the request for measurement, the STA may transmita measurement report to the relay. The relay may determine whether therelay is spatially separated from the other relay based on the receivedmeasurement report, and may allocate a resource for communicationbetween the relay and the STA associated with the relay based on thedetermination result.

In operation 5630, the relay may transmit, to the STA, a beaconincluding information on the allocated resource. The relay mayperiodically or aperiodically transmit the beacon to the STA. The beaconmay include information on a RAW and a slot for communication betweenthe relay and the STA associated with the relay. Information on a RAW ora slot for communication between the AP and the relay may not beincluded in the beacon transmitted by the relay.

FIG. 57 is a flowchart illustrating a communication method performed byan STA according to an embodiment.

In operation 5710, the STA may identify a resource allocated to the STA,based on a beacon received from a relay. The relay received from thebeacon may include information on the resource allocated by the relay.The STA may identify information on at least one of a RAW, a slot, and afrequency subband from the beacon.

In operation 5720, the STA may communicate with the relay based on theidentified resource. The STA may communicate with the relay based on theidentified RAW or slot, or frequency subband. For example, the STA mayreceive data from the relay in a RAW duration in which DL transmissionis allowed, and may transmit data to the relay in a RAW duration inwhich UL transmission is allowed.

The methods according to the above-described exemplary embodiments ofthe present invention may be recorded in computer-readable mediaincluding program instructions to implement various operations embodiedby a computer. The media may also include, alone or in combination withthe program instructions, data files, data structures, and the like.Examples of computer-readable media include magnetic media such as harddisks, floppy disks, and magnetic tape; optical media such as CD ROMdiscs and DVDs; magneto-optical media such as floptical discs; andhardware devices that are specially configured to store and performprogram instructions, such as read-only memory (ROM), random accessmemory (RAM), flash memory, and the like. Examples of programinstructions include both machine code, such as produced by a compiler,and files containing higher level code that may be executed by thecomputer using an interpreter. The described hardware devices may beconfigured to act as one or more software modules in order to performthe operations of the above-described exemplary embodiments of thepresent invention, or vice versa.

A number of examples have been described above. Nevertheless, it shouldbe understood that various modifications may be made. For example,suitable results may be achieved if the described techniques areperformed in a different order and/or if components in a describedsystem, architecture, device, or circuit are combined in a differentmanner and/or replaced or supplemented by other components or theirequivalents. Accordingly, other implementations are within the scope ofthe following claims.

The invention claimed is:
 1. A method of allocating resources in awireless local area network (WLAN) system comprising an access point(AP), a relay, and stations, the method performed by the AP, the methodcomprising: allocating a first resource for communication between the APand the relay, and communication between the AP and a station associatedwith the AP; and allocating a second resource for communication betweenthe relay and a station associated with the relay, wherein the methodfurther comprises: adjusting the second resource allocated for thecommunication between the relay and the station associated with therelay based on power save poll (PS-Poll) information of the station anduplink data indication (UDI) information received from the relay, theUDI information including an amount of uplink data between the relay andthe AP.
 2. The method of claim 1, wherein the allocating of the secondresource comprises allocating at least one of a transmission period anda frequency subband for the communication between the relay and thestation associated with the relay.
 3. The method of claim 1, furthercomprising: transmitting, to the relay, resource allocation informationon the allocated second resource.
 4. The method of claim 3, wherein theresource allocation information comprises information on at least one ofidentification (ID) information of the relay, a transmission allow starttime, a transmission duration, a resource allocation period, anallocated frequency subband, and a station or a relay prohibited fromperforming communication in a predetermined transmission duration. 5.The method of claim 1, further comprising: adjusting the allocatedsecond resource based on interference information received from therelay.
 6. The method of claim 1, further comprising: adjusting theallocated second resource based on station information received from therelay, wherein the station information comprises information on at leastone of a data rate used for the communication between the relay and thestation associated with the relay, and an amount of data transmittedbetween the relay and the station associated with the relay.
 7. Themethod of claim 1, wherein the second resource is allocated by the relayto a restricted access window (RAW) or a slot for the communicationbetween the relay and the station associated with the relay.
 8. Themethod of claim 7, wherein the RAW or the slot comprises a downlinktransmission duration or an uplink transmission duration.
 9. The methodof claim 7, wherein the RAW or the slot determines a time domain inwhich communication is allowed.
 10. The method of claim 1, wherein: theallocating of the first resource comprises allocating a RAW or a slotfor the communication between the AP and the relay and the communicationbetween the AP and the station associated with the AP, and theallocating of the second resource comprises allocating a RAW or a slotfor the communication between the relay and the station associated withthe relay.
 11. The method of claim 1, further comprising: transmitting,to the relay, a beacon comprising information on the allocated firstresource and information on the allocated second resource.
 12. A methodof allocating resources in a wireless local area network (WLAN) systemcomprising an access point (AP), a relay, and a station, the methodperformed by the relay, the method comprising: receiving resourceallocation information from the AP; and allocating a resource forcommunication between the relay and the station associated with therelay based on the received resource allocation information, wherein theallocating comprises: verifying whether the station is spatiallyseparated from another relay, based on a measurement report receivedfrom the station; and allocating the resource for the communicationbetween the relay and the station based on a result of the verifying.13. The method of claim 12, wherein the allocating comprises allocatinga restricted access window (RAW) or a slot for the communication betweenthe relay and the station associated with the relay based on thereceived resource allocation information.
 14. The method of claim 12,wherein the measurement report comprises information on at least one ofthe number of frames transmitted from the other relay, the number offrames transmitted to the other relay, a received channel powerindicator (RCPI) related to a transmission frame of a station associatedwith the other relay, and a received signal to noise indicator (RSNI)related to the transmission frame of the station associated with theother relay.
 15. The method of claim 12, wherein the resource allocationinformation comprises information on at least one of identification (ID)information of the relay, a transmission allow start time, atransmission duration, a resource allocation period, an allocatedfrequency subband, and a station or a relay prohibited from performingcommunication in a predetermined transmission duration.
 16. The methodof claim 12, further comprising: transmitting, to the station, a beaconcomprising information on the allocated resource.